The Tertiary evolution of South Sulawesi: a record in ...searg.rhul.ac.uk/pubs/wilson_bosence_1996...

The Tertiary evolution of South Sulawesi: a record in redeposited carbonates of the Tonasa Limestone Formation

M O Y R A E. J. WILSON & D A N W. J. BOSENCE

SE Asia Research Group, Department of Geology, Royal Holloway University of London,

Egham TW20 OEX, UK

Abstract: South Sulawesi, situated at the junction of three major plates and with an almost complete Tertiary sequence, is an ideal location in which to study syntectonic sedimentation. Redeposited carbonate facies of the lower/middle Eocene to middle Miocene Tonasa Limestone Formation in the Barru area prove to be reliable indicators of tectonic activity. South of the Barru area contemporaneous carbonate sediments formed on a relatively stable shallow-water platform, known as the Tonasa Carbonate Platform. Redeposited carbonate facies and interbedded marls from the Barru area are described and interpreted in this study. The immaturity and provenance of clasts indicate that the redeposited facies were derived from the faulted northern margin of the Tonasa Carbonate Platform. A relay ramp between at least two major NW-SE trending faults is the inferred configuration of this margin. Three main phases of faulting are indicated by the redeposited facies: late Eocene to early Oligocene, middle Oligocene and early to middle Miocene. This is consistent with other outcrop and seismic data from the region and with the inferred plate tectonic situation during the Tertiary.

Sulawesi is located in an exceedingly complex tectonic region, where three major plates have been interacting since the Mesozoic. With reference to the hotspot frame the Pacific-Philippine plate is moving WNW, the Indo-Australian plate NNE and both are colliding with the relatively stable Eurasian plate (Hamilton 1979; Daly et al. 1987, 1991). The convergence zone of this triple junction is a composite domain of micro-continental fragments, accretionary complexes, m61ange terrains, island arcs and ophiolites. Successive accretion from the east of oceanic and microcontinental material, and the associated development of island arcs, have all controlled the stratigraphic development of Sulawesi.

South Sulawesi (Fig. 1), located on the eastern margin of Eurasia, has an almost complete stratigraphic sequence representing the period between the late Cretaceous and the present day (Fig. 2; Sukamto 1975; Hamilton 1979; Van Leeuwen 1981). South Sulawesi is therefore an ideal location in which to study the effects of local or regional tectonics preserved within a sedimentary sequence. Carbonate deposits of the middle Eocene to middle Miocene Tonasa Limestone Formation comprise a major part of the Tertiary succession in the western part of South Sulawesi (Fig. 2). The aim of this paper is to document platform, slope and deep water carbonate lithologies in the vicinity of Barru (Fig. 1), which preserve evidence of local, contemporaneous tectonic activity.

Sulawesi is formed of distinct north-south

trending tectonic provinces (Sukamto 1975). In the west, the north and south arms of Sulawesi are composed of thick Tertiary sedimentary and volcanic sequences overlying pre-Tertiary basement complexes (Sukamto 1975; Van Leeuwen 1981). The Barru area lies within this western arc or province (Sukamto 1975; Hamilton 1979). Central Sulawesi is composed of sheared metamorphic lithologies and in the east a highly tectonized melange complex is present (Sukamto 1975; Hamilton 1979; Parkinson 1991). The eastern periphery of this melange has been overthrust by a dismembered and imbricated ophiolite sequence (Sukamto 1975; Silver et al. 1978; Simandjuntak 1990; Parkinson 1991). Emplacement of this ophiolite and resulting formation of the melange occurred during the middle Oligocene (Parkinson 1991). The microcontinental fragments of the Buton-Tukang Besi Block and Banggai-Sula are thought to have collided with the eastern part of Sulawesi during the early-middle Miocene (Fortuin et al. 1990; Davidson 1991; Smith & Silver 1991) and late Miocene-early Pliocene respectively (Garrard et al. 1988; Smith & Silver 1991). The Tertiary stratigraphy of western Sulawesi is comparable with many of the Tertiary basins in neighbouring east Kalimantan. West Sulawesi, the East Java Sea and east Kalimantan are thought to have comprised a widespread basinal area, the formation of which commenced during the early-middle Eocene (Van de Weerd & Armin 1992).

From Hall, R. & Blundell, D. (eds), 1996, Tectonic Evolution of Southeast Asia, Geological Society Special Publication No. 106, pp. 365-389.

365

2016 at Royal Holloway, University of London on April 15,http://sp.lyellcollection.org/Downloaded from

http://sp.lyellcollection.org/

366 M.E.J . WILSON 8~ D. W. J. BOSENCE

Geology and stratigraphy of South Sulawesi

South Sulawesi is structurally separated from the rest of the western arc of Sulawesi by a NW-SE trending depression which passes through the Sengkang Basin (Fig. 1; Van Leeuwen 1981). Geologically and geomorphologically South Sulawesi is divided by a present day N-S trending depression known as the Walanae Depression (Fig. 1). The Walanae Depression has been described as a major left-lateral strike-slip zone (Sukamto 1975; Van Leeuwen 1981). Seismic (Grainge & Davies 1983) and present-day outcrop constraints suggest significant normal displacement on basin-bounding faults occurred during the Tertiary. The Barru area of this study includes the northernmost outcrops of the Tonasa Limestone Formation and is located on the southern margin of the depression passing through the Sengkang Basin, to the west of the Walanae Depression (Fig. 1).

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Fig. 1. Geological map of the South Sulawesi, showing the location of the Barru area. Modified after Sukamto (1982) and Sukamto & Supriatna (1982).

Two inliers of the pre-upper Cretaceous basement complex of Sulawesi are exposed west of the Walanae Depression (Fig. 1). They comprise tectonic slices of metamorphic, ultrabasic and sedimentary lithologies (Hamilton 1979; Sukamto 1982). Deep marine clastics of the upper Cretaceous Balangbaru and laterally equivalent Marada Formation overlie the basement complexes unconformably (Fig. 2; Van Leeuwen 1981; Sukamto 1982; Hasan 1991). Palaeocene-Eocene volcanics of the Langi Formation and marginal marine siliciclastics, shales and coals of the Eocene Malawa Formation overlie with an angular unconformity the Balangbaru Formation in the eastern and western parts of west South Sulawesi respectively (Sukamto 1982). The upper part of the Malawa Formation interdigitates with shallow marine carbonates of the middle Eocene to middle Miocene Tonasa Limestone Formation to form a transgressive sequence.

Deposition of at least 400 m of shallow marine carbonates occurred in the area between Maros and Tonasa II (Fig. 1; Garrard et al. 1989; Crotty & Engelhardt 1993). These sediments of the Tonasa Limestone Formation are thought to have formed on a relatively stable, gently subsiding, large-scale platform c. 80 km across (personal observation; Garrard et al. 1989), named here as the Tonasa Carbonate Platform. An intra-formational mid- Oligocene unconformity occurs within shallow- water carbonates of the Tonasa Limestone Formation in the eastern Biru area (Figs 1 and 2, Van Leeuwen 1981). From the early Miocene onwards in the Biru area there was a deepening of the environment, and carbonate sedimentation was strongly influenced by local tectonism (Van Leeuwen 1981). This study describes and interprets deep marine late Eocene to mid-Miocene carbonates of the Tonasa Limestone Formation, from the Barru area to the north of the Tonasa Carbonate Platform. During the middle to late Miocene carbonate production was terminated by the influx of volcaniclastic deposits of the Camba Formation. These volcaniclastics were derived from a N-S trending volcanic arc which developed in South Sulawesi (Sukamto 1982; Yuwono et al.

1985). East of the Walanae Depression, lithologies are

quite distinct from those to the west and the oldest lithologies are of Eocene age (Figs 1 and 2; Sukamto 1975). The lithologies are dominated by volcanics and volcaniclastics of the Salo Kalupang, Kalamiseng and Camba Formations (Sukamto 1982; Yuwono et al. 1985). Eocene shallow-marine carbonates of the Tonasa Limestone Formation outcrop only as a fault-bounded sliver at the eastern margin of the Walanae Depression (Fig. 1; Sukamto 1982).



T E R T I A R Y E V O L U T I O N O F S S U L A W E S I 367

WESTERN SOUTH SULAWESI EASTERN SOUTH SULAWESI Age W Formation names. Uthologies E W Formation names, lilhologies E

and thicknesses and thicknesses ' " " ~ ~ TACIP~IW?~.LANAE " Fro. v % . UPPER CAMBA .%%Y, I T . . . . . . . . .

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Fig. 2. Stratigraphic correlation chart of the units to the west and east of the Walanae Depression in South Sulawesi. Based on Van Leeuwen (1981), Sukamto (1982), Sukamto & Supriatna (1982) and Grainge & Davies (1983).

Structure and stratigraphy of the Tonasa Limestone Formation in the Barru area

The Tonasa Limestone Formation in the Barru area is bounded to the south by pre-Tertiary metamorphic and ultrabasic basement lithologies of the Bantimala Block (Fig. 3; Berry & Grady 1987). A smaller inlier (8 km across) of metamorphic basement lithologies, known as the Barru Block (Berry & Grady 1987), is located to the southeast of Barru (Fig. 1). The overall structure of these basement complexes is of relatively rigid blocks tilted to the east and bounded on the remaining sides by eastward dipping thrusts or sinistral wrench faults (Sukamto 1982; Berry & Grady 1989). A number of generally NW-SE trending faults also cut the Tertiary sequence in the Barru area (Fig. 3).

The eastern and southeastern flanks of both basement blocks are unconformably overlain by an almost continuous stratigraphic sequence from the Balangbaru Formation through to the Camba Formation. Tertiary angular unconformities occur at the base of the Malawa Formation and in some

localities between the Tonasa Limestone and Camba Formations. The Tertiary lithologies dip eastwards at 10-25 ° .

North of the Bantimala Block the Tertiary lithologies are folded into a WSW-verging, regional-scale NNW-SSE trending anticline, named here the Rala anticline (Fig. 3). On the northeast limb of the Rala anticline there is a complete stratigraphic sequence from the Malawa Formation through to the Camba Formation, with no apparent unconformities. On the southwestern limb of this anticline Tertiary lithologies dip 20--40 ° to the WSW and the carbonate sequence is considerably condensed or absent. An angular unconformity separates the Camba Formation from the older underlying lithologies on this western limb.

Igneous bodies composed of diorite-granodiorite and trachyte (Sukamto 1982) intrude the Tonasa Limestone Formation and older lithologies in a number of localities (Fig. 3). Although the age of the intrusives in the Barru area is not known, similar lithologies from other areas have been dated using K-Ar techniques as middle to upper Miocene (Sukamto 1982).

The Tonasa Limestone Formation in the Barru area reaches a maximum thickness of 1100 m in the Rala section (Fig. 4). The basal few metres of the carbonate sequence are interbedded with siliciclastics of the Malawa Formation. The earliest carbonate sediments are composed of wackestones, packstones and floatstones (Fig. 4). Some beds contain a rather limited fauna of miliolids, gastropods and occasional pseudomorphs after gypsum or anhydrite. Other facies contain large alveolinids or broken branching corals as well as miliolids. These lower to middle Eocene facies (T a, T. Wonders 1993 pers. comm.) indicate a normal marine back reef-barrier environment with minor restriction. Usually the initial carbonate sediments pass upwards into thick successions of metre-scale bedded packstones and rudstones composed of abundant large Nummulites and coralline algae. The coralline algae often encrust the large benthic foraminifera to form rhodoliths, suggesting shallow marine, relatively turbulent conditions prevailed (Fig. 5a).

In the Rala section only, a subsequent deepening of the environment is indicated by marls and wackestones containing abundant, monospecific, large, flat Discocyclina typical of the lower limits of the photic zone (T. Wonders 1993 pers. comm.). Most areas contain decimetre-scale planar-bedded packages of bioclastic packstones, which include planktonic foraminifera and show occasional evidence of current or wave reworking (Fig. 4). This facies shows an overall fining-upward trend and is interpreted as outer shelf or slope deposits



368 M . E . J . WILSON (~ D. W. J. BOSENCE

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Fig. 3. Geological map of the Barru area with cross-sections (Z-Z', Y-Y'). Palaeocurrent data from the redeposited facies are shown as arrows and rose diagrams. The cross-sections are drawn to scale. The locations of the measured sections (A-B, C-D, E-F) in Fig. 6 and the cross-section (M-M') in Fig. 9 are shown. Measured sections are composite sections along stream cuttings and tracks.



TERTIARY EVOLUTION OF S SULAWESI 369

Lithology Age Facies description

- - -(3oarsev~canic/astic.s of tl~e upper Camba Fm.

---Lower-mbmber-of-the-Camba Fm. - deep marine shales interbedded

_ _ _willa yotc~ielastic_s .........

11051200 [ : i ~ . . . . . . . . . . .

~ NN2- NN6 e/m

1001 . . . . . Miocene

Redeposited carbonate ~ . . . . '~ - facies interbedded with . .

804 . . . . . . . . . . . . . . . . . marls . __^ This section shows the r~-z~, trends in the redeposited 795- m'°hgfacies in the Rala section.

743- ~ The number of beds and E 715 their thickness are not u.

drawn to scale. See Fig. m 649 . . . . . . . . . . . . . . 19 for a more accurate z

representation. O

LU P17 I.Eoc - i

4" /0 . . . . . . . . . . . . . - . . . . . . . . . . . . . . . . . . . . . . . . . ~ l :

4 5 0 ~ '="d"d N15 Decimetre-bedded bioclastic 400 --k~-,-,-,-~, I.Eoc packstones z 375 ~ . . . . . . . . . . . . . . . . . . . . . . . . . . ~

Discocyclina rich marls & 251 - ~ wackestones 2 0 7 ~ . . . . . . . . . . . . . . . . . . . . . . . . . . .

Decimetre-bedded bioclastic M packstones

- - -Num-rhulit~ &fi?J -c-o~M,66 ~ fg-al bioclastic packstones & rudstones

m'-Milio/icl-& a/veo/inid . . . . . . . . C M S f rn c G P C "-. wackestones & packstones

. . . . . . . . . . . . . . . . . . . . . . .

Fig. 4. Simplified composite stratigraphic section of the Tonasa Limestone Formation in the Rala measured section. Location of section C-D is shown on Fig. 3.

with a upper Eocene age (N15, T. Wonders 1993 pers. comm.). In the northern and eastern parts of the Barru area (Fig. 3) these packstones are overlain by a thick sequence of upper Eocene to middle Miocene marls interbedded with redeposited carbonate facies (Fig. 5b), which are the main focus of this paper.

Redeposited carbonate and marl facies of the Barru area

M a r l s

This easily weathered facies is interbedded with coarser, cemented carbonate facies, and is especially abundant in northern and eastern parts of the Barru area. The percentage thickness of the marls in the Tonasa Limestone Formation decreases from the Bangabangae section (E-F; 69% thickness) moving southwards towards the Bantimala Block (Figs 3 & 6). Marls are best exposed in stream cuttings, especially in the Bangabangae section, and although poorly exposed

in intervening areas this facies is considered to be laterally continuous between sections.

The marls are pale green-grey in colour, poorly cemented and often fissile. Planar lamination on a millimetre scale is a common feature of the marls. In some localities the marls appear more homo- geneous, and water-worn surfaces reveal mottling caused by the presence of randomly orientated burrows on a millimetre to centimetre scale. A pelagic biota, including planktonic foraminifera and nannofossils is well preserved and occurs in abundance in this facies.

The fine grained laminated nature of the marls indicates that this facies was deposited in a low energy environment largely from suspension. The presence of abundant, well preserved tests of pelagic organisms indicates deposition in a deep marine basinal setting above the carbonate compensation depth. Burrowing in some localities suggests an aerobic environment.

B i o c l a s t i c p a c k s t o n e f a c i e s

This facies is seen in the upper parts of most sections in the Barru area interbedded with marls and other coarser carbonate facies. The bioclastic packstone facies occurs most abundantly in the Rala section (13.8% thickness of total deeper water facies) and is best exposed in stream sections at this locality (Figs 3 & 6). Although only well exposed in stream cuttings, beds of this facies are thought to be laterally extensive on a scale of tens of metres.

In this facies beds are planar-bedded with bed thicknesses varying from 10-90 cm. Bed contacts are usually planar and sharp. The grain size varies from fine to coarse sand grade between adjacent beds. Sedimentary structures were not observed and burrows with millimetre to centimetre diameters are common in this facies. Although delicate tests of planktonic foraminifera are frequently well preserved, more robust fossils such as coralline algae, large and small benthic foraminifera and echinoids are common as fragments. Based on 'bundling' of beds and grain composition, this facies can be subdivided into two.

(a) Packages of medium bedded packstone which generally lack intervening marly units were found in only one locality in the Rala section (see below, Fig. 12). Faunal elements contained in a single bed are consistently of one age. This subfacies is very similar to the bedded packstones described above, which underlie the marls (Figs 3 & 4).

(b) Single packstone beds interbedded with marls commonly contain both grains which are contemporaneous with and older than the intervening marls. This subfacies often includes



370 M. E. J. WILSON & D. W. J. BOSENCE

Fig. 5. Carbonate facies of the Tonasa Limestone Formation from the (a) lower and (b) upper parts of the Rala Section. (a) Shallow-marine Nummulites and coralline algal rudstone. The coralline algae encrusts the large benthic foraminifera forming rhodoliths. Scale is in centimetres. (b) Typical outcrop of marls interbedded with redeposited carbonate facies. The lower resistant, bioclastic packstone bed is separated from a clast-supported breccia unit by rather easily weathered green-grey marls. Vertical field of view is 1.5 m.

sand grade, angular clasts from all the formations underlying the Tonasa Limestone Formation.

A redeposited origin is inferred for this facies because it is interbedded with basinal marls and contains fragmented shallow-water bioclasts. Sedimentary structures which might indicate the mode of reworking are absent. The packages of bioclastic packstones may perhaps have a similar origin to the outer shelf-slope packstones underlying the marls (Fig. 4). In terms of clast content the single beds of bioclastic packstones are comparable with the graded bioclastic packstone facies described below. Non-graded packstone beds are often documented in sequences containing abundant graded packstones and have been interpreted as grain flow or modified grain flow deposits (Lowe 1976; Cook & Mullins 1983; Gawthorpe 1986; Eberli 1987). However, criteria indicating grain flow deposits such as dish structures, inverse grading, diffuse lamination and outsized clasts (Middleton & Hampton 1976; Cook & Mullins 1983) have not been identified in this facies.

Graded bioclastic pack-grainstone facies

This facies is well exposed and common through- out the upper part of most sections in the Barru area. Graded, bioclastic pack-grainstone facies

are interbedded with marls. Coarser breccia facies are almost invariably overlain by this facies (see below). The percentage thickness of this facies decreases northwards away from the northern margins of the basement blocks (Fig. 6). Beds of this facies are often laterally continuous on a scale of tens of metres, although a 10% decrease in bed thickness over 5 m has been observed.

Bed thicknesses of this facies vary from 5 cm up to 110 cm (Fig. 7). The basal bed contacts are sharp and often planar. Less commonly this facies has an erosive base and exhibits rare groove or flute casts (see below for palaeocurrent data). Beds are graded both in terms of grain size and composition; fining upwards from pebble-coarse sand grade to fine sand-silt grade (Fig. 8a). Heavier gravel or sand grade schist, ultramafic or sandstone clasts tend to be concentrated in the lower parts of beds. Rare water escape structures and imbrication of planar clasts are present. Planar lamination on a millimetre scale is a common sedimentary structure in the upper part of beds (Fig. 8a). The upper bed contact may be planar or slightly undulose and sharp or gradational into marls.

This facies incorporates a large variety of often fragmented bioclasts, including large and small benthic foraminifera, coralline algae, echinoderm and very rare coral debris. It contains up to 25% well preserved planktonic foraminifera, especially in the upper finer part of beds. Lithic clasts include




N ,~ 10km ~ 5km .~ Bangabangae section Rala section

F Upper coarse volcaniclastic Dm! B m i "~"~"~"~"~ '~ member of the Camba Fm. ~ , , ~ , , ~ , - ~ m

775 ~'1 Lower member of the Camba 1 2 0 0 [ ' l 520.

1 Fro. - Deep madne shales ~4n= I.'.~ 425

interbeclded with volcaniclastics . . , , , - ' - ' - - - - - - - - - - - - . . . . . . . . . . . . . . . . .°_ . . . . - . . . . -~- . . . . -~- . . . . _---

488 ~ ' " - ' " ' - ~~~-~'""~-~" "~"~ 207, Redeposited carbonate ,,'A facies interbedded with /'

~ ~ marls of the Tonasa ~_ . . . . . ' "~ ,o Limestone Fm. ,,'"

78 ~ ~ - - - -t::::! ,,

. . . . . . aliow-wa ei acl;soit -;- ona . . . . . . . . . . . . . .

E ~ M S f m c G P C Limestone Formation C I I~ s f' m c G P C:

Ban~labangae section 408 m

Clast-supported breccia Graded bioclastic packstones topping the above Marl supported breccia Graded bioclastic packstone

Rala section

S Doi-doi section

, , , , M S f m c G P C

Doi doi section Total thickness of made & redeposited facies 635 rn 218 m Total number of redeposited beds 76 173 66

39.64 58.51 11.85 0.40

0.93 0.47

12.63 8.82

20.14

4.35 Bioclastic packstone 6.17 13.77 7.26 Planktonic foraminifera wacke/packstone 7.82 1.10 5.62 Mad 69.02 20.22 4.13 Other 6.76 0.40

% % of limestone conglomerates, packstones and marls 100 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ~ . . . . . . . . . . . . . . . . . . . .

I " ' : : : : : : : : . M a r l : : : : : ~ . . . . . . . . . . . . - _ . , ~ . v . y . - . . . . . . , . . d . . ~ ~ . r ~ ~ 50 ' - . . . . . . . . . . . . . ¢ " ¢ ' " " ' ~¢ " " "

0 % % Amalgamation of redeposited carbonate beds

100 5O 0

DISTAL ~ '

BASlNWARD

PROXIMAL

Fig. 6. Three composite stratigraphic sections through the redeposited facies interbedded with marls showing northwards proximal to distal and basinward trends. See Fig. 3 for location of the stratigraphic sections (A-B, C-D, E-F).

metamorphic (see below) and quartzose sandstone lithologies, a wide range of limestone facies and marl clasts. Both packstone and grainstone textures occur, although in the majority of beds the matrix is marly or composed of finely fragmented bioclasts.

Trace fossils on a millimetre to centimetre scale, including Taphrhelminthopsis are common at bed contacts and may be parallel or perpendicular to bedding. Silica replacement is frequent within this facies and occurs in three main forms: as chalcedony within individual bioclasts or litho-

clasts, as nodules and as irregular but apparently continuous 'beds'. Silica nodules are parallel to bedding, up to 15 cm thick and 50cm across and sometimes follow centimetre diameter burrows.

Because this facies is interbedded with basinal marls and contains fragmented lithoclasts and shallow marine bioclasts, it is considered to be redeposited. Sedimentary structures such as an erosive base, normal grading and parallel lamination are typical of calciturbidites (Crevello &



372 M . E . J . W I L S O N ( ~ D, W, J, B O S E N C E

Graded bioclastic pacidgrainstone facies

T l - - - -

8

m

~ |......~... .....

6) Upper bed contact is planar or slightly

i i i i i i i i i l overlyingUndul°se and sharp or gradational i n t O m a r l s

' k 5) Millimetre scale parallel ~ laminations

% . 4 ) Rare water escape structures

' i ~ i ~ i ~ i ~ i ~ i ~ i ~ 3) Normally graded ' i ~ i ~ i ~ i ~ i ~ i ~ i ~ ' i ~ i ~ packstone fining upward ..~.~.~,.~.~.~.~.~.~.~.~. <~<~<~<.<~<~<~<~<~<~ from grave l / coarse sand to . ~ -i~ ~-~ ~'~"l~'~'~"l~"l~'~ • < ~<~< ~< ~< ~ ( ~ < ~ < . < ~ < ~ fine sand/slit, ,.~-~.~.~.~.~.-~.~.-i~.~.~.~-~

.. ~ • {'~ • ~ • ~ • ~ • ~. ~; ~.'.~,'-~,'- ~ ~ ~',,'~ imbrication

.,~.~.~-~-i~. .~'1~-~'1 , ~ , . , ~ , ~ , ~ ; , : , ~ ,, sharp o.an '¢t:< t : < E ¢ E d . ~ ~ ( ~ E ( ~ ~ lanar base to bed . . . . . . . . . . . . . . . . . . . . ~._ p • -'"'""-":~ with rare groove or ............. "1 f's gs (~ flute casts.

Planktonic foraminifera wacke/packstone facies

l:i::i::i::3

I

M

5) Planar sharp or transitional contact into marls

, ~ , ~ 4) Grain- or matrix-supported ~ in a marly matrix

~ ~ 3) Well preserved planktonic ~ % % ~ foraminifera comprise 70-90 ~%~s=~%~, % of the grain types.

~;%%%%%~ 2) Normal grading from ~ ~ ' ~ medium sand ~lrade to silt ~ _ ~ . ~ . ~ - _ . ~ grade is occas,onally ~ _ ~ _ ~ _ ~ seen. Other beds appear

-~-~-~ ~-~ ungraded

, ~ = ~ - ~ ; ~ ] ~ 1 ) Planar sharp or ~ - ~ L ~ . I transitional basal contact I i i i silt fs ms cs

M

Clast-supported breccia facies topped by a graded bioclastic pack/grainstone facies

7) A graded packstone facies '<~.~!~-~ (see above) almost invariably '~<'~,.~ overlies the coarse limestone ' ~ conglomerate

' i ~ i ~ 6) Relatively sharp contact

~ ¢ 1 ~ .o. ¢1 ~. ~ m . . . . ~i;~: .... " ;~ '~ :~:~:~i~ 5) Shght fining upward of ~(~ ,~ : ;~; : °. '~:?.o:Z :~.~.~ angular clast-supported :;:.~.~{6 .,~.,'~.~ :U~ ~:~!~; ~ :$ breccia.

::_~DS;;(S:m;:~;~".~:~!:~ 4) Clast s i z e varies ?~!6! : 'o !~ :~9 ' . : :~ !~ : '~ :~ :~ from 4 m across i ~ : ~ : i ~ ' ~ : ~ ) ~ ) , ~ : ~ down to fine sand !~.~:~/:?~ ;~ i:~!~: :~ i ~ :~:~fi ~ grade

!i~;'.~i~:~,:~i~'~<~-~ :~i~i~ii~ l 3) Common circum-clast ~~:~_:~9.i~i~I~:~~:~_:~( ~. ~ stylolites and rare clast i~.:.~;~':-~.~'!~.:~, '~ ~ ~l imbrication.

~ . ~ b ~ £ ) ~ ! 6 ~ : 2 : ~ !] 2) Coarsening upward at ,~§~'/~i6-.:~?0?~b:~!:~ I base may occur.

1 ~ ~narp, planar or irregular base

fs cs G C

Marl-supported breccia facies topped by a graded bioclastic ~iiiiiil il pacWgrainstone facies

~i~2 ~- , ,~- , ,~ 5) Sharply overlain by graded

~ ;~ ;~ :~ :~x packstone facies (see above left). "~!'-'! ~!"! ' - ' !~ ' -3 . : : : = . . . . . . . .d ~ . - - . ~ . - . - ~ " ~ " ~ 4) Chaotic poorly "'"~7 T"' I .~. , ' [ 1:%1 sorted facies which :: '" ',~.,.. 'L.'._"'_" _ "'~ ,1:.":.1 lacks any signs of

~ " ~ / ~ ~ ) ! ~ ! , ~ ) ( . ~ ( . ~ t packst0ne channel, ~ r ~ t . . ~ . ~ . ~ ( . ~ , l which includes cross t ~ ~ lamination and clast / ~ . . . : ~ : : . ~ imbrication.

~ - - : : : : I =~ Sub-angular ~ - ' - J ~: ' - '1 clasts up tO 1 m ---7 -/~ "N-..7 ~'-": I across mostly 7" ~.-I J':':l supported by a

~ 1 ~) Sa~ a~gr~t~tct dulOse

M fs cs G C

Fig. 7. Schematic diagrams showing the main features of four of the redeposited facies. The bioclastic packstone facies are not shown as they are planar bedded and lack other visible sedimentary structures. Diagram not to scale.

Schlager 1980; Cook & Mullins 1983; McIlreath & James 1984). A complete Ta__e Bouma sequence (Bouma 1962) characteristic of siliciclastic turbidites is not seen in this facies. Incomplete Bouma cycles are a common feature of other modern (Schlager & Chermak 1979) and ancient redeposited carbonates interpreted as calciturbidites (Pfeil & Read 1980; Mcllreath & James 1984; Gawthorpe 1986; Eberli 1987; Braithwaite & Heath 1992; Herbig & Bender 1992). Since skeletal carbonate grains are ofter~ porous or irregular in shape, grain size distribution and sedimentary structures in calciturbidites are commonly less regular than in siliciclastic turbidites (Tucker & Wright 1990).

The radial chalcedony preserving 'ghosts' of earlier bioclasts and the smooth irregular shape of nodules both indicate the secondary replacement nature of the silica in this facies. Probable sources

of the silica are sponge spicules and microfossils, present in both the marls and packstones, and lithoclasts such as quartzose sandstones present in the redeposited carbonate facies. The Tonasa Limestone Formation is similar to a number of other ancient carbonate deposits in which it is reported that redeposited facies are the only carbonate facies in which silica replacement is common (Gawthorpe 1986; Bustillo & Ruiz-Ortiz 1987; Coniglio 1987; Eberli 1987; Reijmer & Everaars 1991; Herbig & Bender 1992). Silicification is thought to be prevalent only in the redeposited facies because the rapid burial of transported siliceous tests and clasts prevents the dis- solving silica passing into the overlying seawater (Bustillo & Ruiz-Ortiz 1987). Certain horizons or burrows perhaps had a higher original porosity and the silica has preferentially remobilized to these areas during diagenesis.




Clast-supported breccia facies

This sedimentary facies is interbedded with marls and bioclastic packstones and occurs particularly abundantly in localities close to the northern margins of the basement blocks (Fig. 3). In the Doi-doi section (A-B) this facies comprises 58.5% of the thickness of the deeper water carbonate facies (Fig. 6). Beds are laterally continuous on a scale of tens to hundreds of metres. This facies is almost invariably capped by graded bioclastic pack-grainstone facies (described above) and the contact may be sharp or transitional over about 10 cm.

Usually the sequence of clast-supported breccia topped by a graded bioclastic pack-grainstone facies is between 70 cm and 5 m thick, though units up to 25 m thick do occur (Fig. 7). The basal contact of this breccia facies is usually sharp and may be planar or more irregular. In rare cases, this facies exhibits a transitional basal contact with marls, in

which up to 30 cm of the lowermost part of the bed contains up to 25% of the green-grey marl as a matrix. The lower part of the sequence is a coarse, clast-supported breccia with angular-sub-angular clasts usually up to 60 cm across. In thicker units the maximum clast size seen is 4 m across. The bioclastic packstone matrix of this facies is rarely seen due to circum-clast stylolites which give a fitted fabric to the breccia. Locally, this facies may coarsen upward over the lower 40 cm (Fig. 7). More usually there is a slight fining upward of clast size through the breccia facies. Rare imbrication of planar clasts does occur. Replacement or partial replacement of clasts by silica is sometimes seen within this facies (see above). A wide variety of lithic clast types is present in this facies (Fig. 8c). These include metamorphic, igneous (see below) and quartzose sandstones lithologies, and a range of shallow-water wackestone, packstone and grainstone and deeper-water marl clasts. Matrix comprises a relatively low percentage (2-8%) by

IIO !iii~iiiiiiiiiii~ii!i~ ~ ~i ~ ̧ ~̧̧~ ...... ,i~ii! i ¸~ii~i ~ ........... ~ .............. ~ ~i!i~ ~ % ~

Fig. 8. Photographs of the redeposited carbonate facies. (a) Graded bioclastic packstone bed, showing fining upward and parallel lamination at the top of the bed. Darker grains are formed of older non-carbonate lithologies. Scale is in centimetres. (b) Amalgamation of clast-supported breccias topped by graded bioclastic packstone unit. The lower coarse, angular clast-supported breccia is sharply overlain by a graded bioclastic packstone unit. Not that the parallel lamination in the graded bioclastic packstone becomes closer together as the unit fines upwards. The bioclastic packstone is sharply overlain by another clast-supported breccia layer. (c) Outcrop of angular clast-supported breccia showing the variety of clast types present within the redeposited carbonate facies. The dark clasts are schists and ultrabasics and were derived from the older formations in South Sulawesi. Clasts from a range of shallow-water carbonate facies and small rip-up clasts of basinal marls occur in abundance. Scale is in centimetres. (d) Photo- micrograph of a bed of planktonic foraminifera wacke-packstone. Scale bar is 1 mm across.



374 M . E . J . WILSON t~ D. W. J. BOSENCE

volume of the breccia layer and is composed of marl or finely fragmented clasts or shallow-water biota. Although this sequence of units is interbedded with marls, amalgamation of both the breccia and overlying graded packstone facies frequently occurs, especially adjacent to the northern margins of basement blocks (Fig. 8b). Sometimes a coarse breccia directly and sharply overlies another breccia and the packstone facies is missing.

This facies is redeposited because it is interbedded vdith basinal marls and contains a variety of coarse lithoclasts and fragmented shallow-water biota. Clast-support, poor sorting, occasional inverse grading and clast imbrication suggest transport and deposition from a lower traction layer (Lowe 1982; Pickering et al. 1986; Tucker & Wright 1990). Circumclast dissolution has removed much of the matrix (cf. Davies 1977). Debris flows, which occasionally show inverse grading at the base, can transport coarse material with as little as 5% matrix (Rodine & Johnson 1976; Picketing et al. 1986). However, normal grading of clasts towards the top of breccia units argues against a debris flow as the mode of origin. A high density turbidity current with a lower inversely graded R 2 layer and upper normally-graded R 3 layer (cf. Lowe 1982; Tucker & Wright 1990) is inferred for the transport and depositional origin of this facies.

After deposition of the coarser breccia material, the graded bioclastic packstone capping this facies is thought to have been deposited out of suspension from turbulent flow. An analogous experimental example of a high density turbidite topped by a lower density turbidite has been described by Postma et al. (1988). Many examples of two layer carbonate sediment gravity flows have been described from ancient (Cook & Taylor 1977; Hubert et al. 1977; Cook 1979; Johns et al. 1981; Kepper 1981; Hiscott & James 1985; Gawthorpe 1986; Eberli 1987; Watts 1987) and modern (Mullins & van Buren 1979; Schlager & Chermak 1979) settings. Turbidity flows are often entrained on top of coarse gravity flows and can be generated by reverse shear at the flow-water interface in the head region of the coarse flows (Hampton 1972). A genetic relationship is therefore suggested between the clast-supported breccia topped by the graded bioclastic pack-grainstone facies and the graded bioclastic pack-grainstone facies (see below).

sharply overlie the marl-supported breccia facies in both outcrops.

Bed thicknesses of this facies are up to 2 m, with sharp and undulose bed contacts (Fig. 7). In this poorly sorted facies sub-angular clasts up to 1 m in diameter are present (Fig. 7). The matrix is composed of marl, and both matrix and clast- supported fabrics occur, although the former support mechanism is more common. One bed contains a N-S orientated, flat-topped channel 60 cm deep and 2.5 m wide, composed of breccia fining upward to a grainstone. Internal sedimentary structures within this lensoid body include planar cross-lamination and a layer with abundant marl clasts, some of which show imbrication. A large variety of sub-angular limestone clasts, including wackestones, packstones and float-rudstones occur within this facies. Large rounded clasts of green-grey marls and clasts of graded bioclastic packstone and clast-supported limestone breccia occur.

The massive, chaotic, poorly sorted, nature of this facies and presence of large sub-angular clasts floating in a marly matrix are features typical of debris flows (Cook et aI. 1972; Middleton & Hampton 1976; Lowe 1979, 1982; Cook & Mullins 1983). In debris flows the cohesive strength of a fine sediment-water matrix is sufficient to support and transport large clasts on slopes as low as 1 ° (Cook et al. 1972; Prior & Coleman 1982; Hiscott & James 1985). The range of clast types indicates that both shallow and deeper water carbonate lithologies were incorporated into this facies. Since clasts of reworked breccia or packstones were not seen in other redeposited facies, a deeper water origin for this facies is suggested. Modern mud- supported and clast-supported debris flows occur in proximal and distal parts of the lower slope of the Bahamas respectively (Mullins et al. 1984).

Graded bioclastic packstones capping debris flow deposits have been described from other modern and ancient deposits (Crevello & Schlager 1980; Mullins & Cook 1986). Channels containing graded lenses of carbonate sands within debris flows are less commonly reported (Braithwaite & Heath 1992). It has been suggested that turbulence may have played an important role in supporting grains at the top of flows (Cook et al. 1972; Hampton 1972). The channelized normally graded body within this facies perhaps indicates amalgamation of the breccia.

M a r l - s u p p o r t e d breccia f ac i e s

This facies occurs in only two localities in stream cuttings in the Rala section (Figs 6 & 12). This facies is laterally continuous on an outcrop scale (m). Graded bioclastic pack-grainstone facies

Plank ton ic f o r a m i n i f e r a w a c k e -

packs tone f a c i e s

Although this facies occurs in the upper part of all sections in the Barru area, it is best exposed and




occurs most commonly in the Bangabangae section (E-F) where it comprises 7.8% of the thickness of the deeper water facies (Fig. 6). This facies outcrops in stream cuttings and is only known to be laterally continuous on an outcrop scale (m).

Planar beds of this facies between 20 and 60 cm thick are interbedded with marls (Fig. 7). This facies differs from the marls in that it is cemented and contains a higher percentage of planktonic foraminifera and fragmented shallow-water biota. Upper and lower bed contacts are planar and may be transitional or sharp with interbedded marls. Normal grading, fining from medium to silt-size, is occasionally seen (Fig. 7). Well preserved planktonic foraminifera comprise 70-90% of the bioclasts present in a micritic or marly matrix (Fig. 8d). Fragmented echinoderms, benthic foraminifera and coralline algae form the remaining bioclasts. Silica nodules parallel to bedding are present within this facies.

The normal grading sometimes seen in this facies suggests deposition by waning current flow. Reworking could also account for the increased concentration of planktonic foraminifera and presence of fragmented shallow-water bioclasts, relative to the intervening marls. Although sedimentary structures which could differentiate between storm, contour currents or mass flow processes as the mode of reworking are absent, the location of this facies relative to other redeposited facies suggests a mass flow depositional origin (see below).

Origin of the redeposited carbonate facies

Redeposited carbonate facies have been related to slope instability (Hopkins 1977; Schlager & Camber 1986), eustatic sea-level changes (Watts 1987; Reijmer et al. 1988, 1991, 1992; Burchell et al. 1990; Reijmer & Everaars 1991; Herbig & Bender 1992) or tectonics (Bosellini 1989; Fernandez-Mendiola & Garcia-Mond6jar 1989; James et al. 1989; Playford et al. 1989; Elmi 1990; Garcia-Mond6jar 1990; Kenter et al. 1990; Watts & Blome 1990; Everts 1991). In this section it is shown that the majority of the redeposited facies in the Barru area are derived from a tectonically active faulted platform margin. Downcurrent changes in the organization of the redeposited facies are also discussed below.

Subdivision of the redeposited facies

Redeposited carbonate facies interbedded with basinal marls are located in the upper parts of sections in the northern and eastern parts of the Barru area (Fig. 3). West of the Rala anticline

redeposited facies interbedded with marls are considerably reduced in thickness or are absent (Fig. 3). In terms of spatial distribution and basement clast content the redeposited facies can be subdivided into two groups (Fig. 3). (1) The Bantimala redeposited facies are located to the north and east of the Bantimala and Barru Blocks respectively. This facies group contains basement clasts of lithologies, such as quartz-mica schists and ultrabasics, which outcrop in the northern part of the Bantimala Block. (2) The Barru redeposited facies crop out only to the north of the Barru Block. These facies contain basement clasts of lithologies such as serpentinite and granite-granodiorite, which are present in outcrops within the northern margin of the Barru Block.

Proximal to distal changes

In the Bantimala redeposited facies the total thickness of marls and redeposited facies thickens and then thins towards the north over a distance of 15 km (Fig. 6)~ When the thickness of redeposited units is expressed as a percentage of total stratigraphic thickness there is a clear decrease in redeposited carbonate units, relative to marls, towards the north (Fig. 6). Correspondingly the percentage of amalgamated redeposited carbonate beds also decreases towards the north (Fig. 6). These factors indicate proximal to distal and basinward trends towards the north.

The occurrence of a clast-supported breccia topped by a graded bioclastic pack-grainstone facies suggests a genetic relationship between this sequence and single beds of the graded bioclastic pack-grainstone facies. The spatial distribution of facies (Fig. 6) might also suggest a downcurrent change from a two layer into a single layer sediment gravity flow deposit. Downcurrent or lateral changes of two component gravity flows into single layer flows have been reported from both modern and ancient carbonate deposits (Davies 1977; Cook 1979; Krause & Oldershaw 1979). The planktonic foraminifera wacke-packstone facies may be the correlative distal deposit of the graded bioclastic pack-grainstone facies (cf. Davies 1977). Outcrop constraints preclude the possibility of proving this inferred proximal-distal facies relationship.

Nature o f clasts

The majority of lithoclasts in the redeposited facies are angular to sub-angular, often with the clast margin cutting across the grain fabric. A continuum of clast sizes ranging from 4 m down to fine sand grade are present. A wide variety of clast types occur in both groups of redeposited facies (Fig. 8c).



376 M.E.J. WILSON & D. W. J. BOSENCE

Schist, serpentinite, ultrabasic, quartzose sandstone and shale clasts were derived from the underlying formations. A range of limestone clasts which vary both in terms of age and environment of deposition are also present in the redeposited facies. Often a redeposited bed will contain limestone clasts which are both contemporaneous with and older than the intervening marls. Rip-up clasts of marl are often found within the redeposited facies.

Tectonic versus eustatic origin

The deposition of the redeposited facies may have been triggered by eustatic or tectonic events. The variety of clast types excludes other possible causes, such as gas charging, tidal or surface wave action, rapid deposition or patchy shallow marine cementation resulting in unstable slopes. A number of factors, outlined below, exclude the possibility of a eustatic mechanism as the main cause of the majority of the redeposited facies.

Shallow-water carbonate lithologies in the Barru area and on the Tonasa Carbonate Platform to the south, with the exception of the lowermost beds in the carbonate sequence and some beds in the Doi-doi section, lack lithic grains. It is therefore suggested that no major areas of basement highs existed during the deposition of Eocene shallow- marine carbonates. Erosion of basement lithologies or siliciclastic grains from carbonate deposits due to sub-aerial exposure would have required the removal of between 60-470 m of shallow-water carbonate deposits. This is much greater than, or close to, the inferred maximum for, short-term sea-level falls for the Tertiary, the value of which is thought to vary from 75-100 m (Haq et al. 1987; Sarg 1988). Limestone clasts in the Bantimala redeposited facies contain no evidence for sub- aerial exposure until the latest Oligocene. Prior to the deposition of marls during the late Eocene, both the Barru area and the area of the Tonasa Carbonate Platform were the sites of widespread accumulation of shallow-water carbonates. During the late Eocene rapid deepening occurred in the Barru area, whilst shallow marine sedimentation with only localized evidence for Oligocene karstification continued on the Tonasa Carbonate Platform.

The range and immaturity of clast types within the redeposited units suggest derivation from a tectonically active faulted margin of a carbonate platform (cf. Kepper 1981; Hurst & Surlyk 1984; Martini et al. 1986; Eberli 1987; Burchette 1988; Eaton & Robertson 1993). Carbonate slopes become unstable at angles of 30-40 ° (Kenter 1990). Derivation of the redeposited carbonates is thought to be related to oversteepening of the

platform margin caused by faulting. The underlying formations are relatively easy to erode and under- cutting of the platform margin may also have contributed to the oversteepening. Provenance studies, the spatial distribution of redeposited facies and field evidence outlined below, indicate that the redeposited facies were derived from the northern faulted margins of the Bantimala and Barru blocks.

A eustatic control or enhancement of a tectonic control cannot be dismissed for some of the redeposited facies. Increased shallow-water carbonate production and 'shedding' into deeper water areas, caused by increased accommodation space and more favourable conditions may be related to eustatic changes. For example, packages of decimetre bedded bioclastic packstones, which only contain fossils contemporaneous with the adjacent marls, may be related to eustatic changes (cf. Reijmer et al. 1988; 1991; 1992; Watts 1987; Burchell et al. 1990; Reijmer & Everaars 1991; Herbig & Bender 1992).

Field evidence for derivation from a faul ted

platform margin

No complete sections through the Barru redeposited facies are exposed. In general, the maximum clast size decreases and the bed thickness of these redeposited facies thins towards the north (Fig. 9). These factors indicate basinward and proximal to distal trends towards the north away from the Barru Block within the Barru redeposited facies.

The Barru Block is bounded to the north by a fault downthrowing and dipping steeply (60-70 °) towards the NE (Fig. 3). This fault juxtaposes basement lithologies in the footwall against coarse redeposited facies of the Tonasa Limestone Formation in the hanging wall (Fig. 9). Although this suggests normal fault movement, kinematic indicators were not seen and the fault surface itself is not exposed, so it is not clear if oblique-slip was also involved. All the basement and limestone lithologies reworked into the Barru Redeposited Facies outcrop in situ within or adjacent to the margins of the Barru Block (Fig. 3), suggesting local derivation. These facts strongly suggest that the area of the Barru Block was the site of shallow- water carbonate accumulation and the Barru redeposited facies were derived from an active syn-depositional faulted margin to the Barru Block.

No similar fault is exposed juxtaposing lithologies of the Bantimala Block against redeposited facies south of Rala. In part this may be due to outcrop constraints, with the upper volcaniclastic member of the Camba Formation unconformably overlying much of the northern edge of the




SSE NNW

~ ...... Erosion of footwall , , %" ,, ~' ,,:~.--~--k , ,-~ %" ,~ <--~-~-~--~ ' i lithologies into the , ,'%',', ,', ,', t , s, s%',', , ' ~ , ' % ' ~ t % ' t ~ s % ' ~ 1 ~ ,~ hangingwall area Present day

,, z...~.,~,, ,, ,, ,, ,, ,, ,,~¢...,¢_.~ ,, ,, ,,1 l i b , . . . . . . . . . . . . . land surface ,

% %" %'~1,~ % % Y + 4~ % % % % % % % % % | ~ . . . . . . . . . . . . . . . . . . . . .

, ' , ' ,~' , ' , '4°,%~,' ,g$,, ' , ' , ' , ' ,~, I V ~ . . : . . : - . = . :

% % % % % % i ~ % " . . .. ':':.:'.~""%"::i:(.:.!!-:i::~: ~i)!~ :: .... • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . / % %" '% % % %" = : . .::.. <: .:"~;4.~.~.:::: .I:.::+-. , , , , , o , . , , , , , . . . . . . . . . . . . . . . . . . . . . . . . . , , , , . . . . . . . . . . . . . . . . . . . . . . . .,. ,,- .,, ,,, .,. ,., ke - :: . . , ':~:~,?i!:~i~!:~::?~i~!i?i!~.~... ~ . . . . . . . . . . . . . .

i ~ ~ ~ % ~ @ @ @ i ~ ~ ~ ! % % %, % % % % . .::. .~ . . . . . L : : ::~:~.?~:;-:?:.:~-¢..., .... • . . . . . . . . . . . ! i l i , . . . . . . . . . . . . . . ,o,o,, . . . . . . . . ~:~E

• " . " . ~ ". ~ [ ~ " ~ +. ÷ Y . ". "'1~. "..Z'. ' ~ . ~ ~ . . . . " , , ' , , ' , , ' , , ' ~ , , ~ , , ' ~ k ~ ÷ ' ÷ ' ~ , ' , , " , , ~ , ' , , ~ , " ~i i~!~i: :~.~i~!~ --- - - - - - - - -=-- - - - - - - - - -""" ' "" I % % % % % % % % ~ @ ÷ 1 % % %1~l,~ % ~ % ~ ~ ' ~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I

~ ~.%' .~ % % ~ . ~ ÷ +~. ' ~ . ~ . ~ ' . " . ~ ~ ~ ................................ I % % % % %" % % % % ~ + + ~ % % % % % ~ ~ ~ . . . . . . . . . . . . . . . I

% % % % % % % % % ~ @ ~ % % % % % % % % 1 " . . . ~ :2 . . ; . . , . ' . . :; :::.. ,.. i::.. , ; . . * ~ . . . . . . . . l.i i i I ] ' l i"" "l . . . . . . . . . . i i .

310/60-70 ° Underlying lithologies not exposed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ; Main fault ' ,KEY

M~::ld;posited packstonesand I ~ i oE 200"1 matrix to the limestone bm~ia/~ ~ ~I 100"t Shallow marine carbonates / ~ E ~1 E o50-1 Intrusive - pre-Tertiary ' -~u'! .E_=N 104 " ~ " ~ ' ~ ~ - ~

[~-~ Calcite-veined metamorphic ' , : ~ 11

,_____ba s_~_m_~_n_t-_pr_~-_T_e_rtia~_ . . . . . . . . . ~ 0 160 250 560 1600 2000 4600 8000 -~ Distance away from fault (metres)

Fig. 9. Schematic cross-section through the northern bounding fault to the Barru Block, showing redeposited facies thinning and fining towards the north away from the fault. See Fig. 3 for location. Not to scale.

Bantimala Block (Fig. 3). Faults south of Rala with similar trends as the north-bounding fault to the Barru Block may have acted as sources for the redeposited facies. However, movements on these faults contemporaneous with deposition of the Bantimala redeposited facies cannot be proved.

Configuration of the faulted platform margin

Redeposited facies are inferred to have been sourced from at least two faulted northern margins of the Barru and Bantimala blocks. The lack of channelization and facies distribution suggests that both groups of redeposited facies were derived as sheets of carbonate debris from a faulted line- source forming base-of-slope carbonate aprons (Mullins & Cook 1986). The Barru redeposited facies are inferred to have been derived from the fault which today delimits the northern edge of the Barru Block. The precise area and fault for derivation of redeposited facies from the northern edge of the Bantimala Basement Complex is less clear. Regional geological observations and palaeocurrent data can be used to define possible configurations of the platform margin and to relate the two source areas.

Derivation

On the eastern limb of the Rala anticline the lower marine member of the Camba Formation con- formably overlies the Tonasa Limestone Formation (Fig. 3). On the western limb of this anticline the lower marine member is absent and an angular unconformity separates a condensed sequence of the Tonasa Limestone Formation, or older formations, and the upper volcanic member of the Camba Formation. The lack of abundant limestone clasts in the volcaniclastics directly above this unconformity suggests that major erosion had occurred prior to the deposition of the Camba Formation. This angular unconformity may therefore have been generated during the Eocene to Miocene and supplied material for the Bantimala redeposited facies.

Two kilometres south of Doi-doi is a fault with a trend similar to the north-bounding fault of the Barru Block (Fig. 3). This normal fault dips to the NE and juxtaposes basement lithologies against the Balangbaru Formation. Southwest of this fault a thin layer of the Malawa Formation and upper Eocene packstones of the Tonasa Limestone Formation unconformably overlie metamorphic lithologies of the Bantimala Block. The packstones are in turn separated from the upper volcanic



378 M.E.J. WILSON & D. W. J. BOSENCE

member of the Camba Formation by an angular unconformity. The eastern part of this fault, which does not penetrate the Camba Formation, is intruded by a later diorite stock. The offset of the N-S trending contact between the Malawa and Tonasa Limestone Formations north of this intrusion indicate normal or possibly strike-slip movement on the fault (Fig. 3). South of the intrusion the Balangbaru, Malawa and Tonasa Limestone formations are all present. The Tonasa Limestone Formation in this location is composed of 310m of shallow-water Eocene-Oligocene carbonates overlain by 50 m of deeper water carbonates dated as Oligocene (E. Finch 1993 pers. comm.). This block bounding fault and/or other similar trending faults in the vicinity or under the Camba Formation are inferred to be the northern faulted margin of the Bantimala Block, which shed material forming the Bantimala redeposited facies.

Palaeocurrent data

The Bantimala redeposited facies thin and fine northwards away from the Bantimala Block (Fig. 6). Rare clast imbrication and scour structures (cf. Hubert et al. 1977; Hiscott & James 1985), indicate that the transport direction of the redeposited facies had strong northerly, northnorthwesterly and easterly trends (Fig. 3). Although palaeocurrent data are scarce, the southern area shows a dominant transport direction towards the east (Fig. 3). In the northern area finer redeposited facies tended to be north-directed and are inferred to have been derived from the Bantimala Block which lay to the south. Coarser redeposited units in the north tend to be

easterly directed and are thought to have been derived from the northern margin of the Ban'u Block, an inference supported by clast provenance data (Fig. 3).

Evidence for Tertiary exposure

Carbonate lithologies are poorly exposed along the margins of the basement blocks close to the north- bounding faults of the Bantimala and Barru blocks. Limestone clasts reworked from these footwall blocks, however reveal evidence of karstification and subaerial exposure. Limestone clasts derived from the Barru Block during the late Eocene (NP17-19, E. Finch 1993 pers. comm.) contain features such as irregular dissolution hollows lined by blocky cement and then infilled by fine carbonate silts and micritic glaebules (Fig. 10a). The margins of clasts cut across all of these early diagenetic features, suggesting subaerial exposure of the footwall area of the Barru Block. Limestone clasts in the Bantimala redeposited facies do not show corresponding evidence for sub-aerial exposure of the Bantimala Block until the latest Oligocene.

Regional tilting

A number of factors suggest that the whole of the Barru area was tilted towards the east during the deposition of the Tonasa Limestone Formation. A thinned carbonate sequence, the angular unconformity with the overlying Camba Formation and absence of the Balangbaru Formation in the western part of the Bantimala footwall block all

Fig. 10. Photomicrographs showing features of the redeposited facies. Scale bar is 1 mm across. (a) Shallow-water carbonate clast showing evidence for karstification. An irregular dissolution hollow has been coated in a blocky cement, subsequently fine sediment has infilled the void and there is a final phase of sparry calcite cement at the top of the cavity. (b) Quartz mica schist derived from the pre-late Cretaceous basement complex adjacent to an Eocene large benthic Discocyclina foraminifera. Sample from a graded bioclastic packstone bed from the Bantimala redeposited facies.




suggest that erosion was more effective to the west. Only the Barru Block underwent sub-aerial exposure from the late Eocene. From the late Eocene onwards, west of the Rala anticline, redeposited facies are considerably reduced in thickness (< 45 m) or absent compared with those to the east (up to 635 m). This indicates much greater accommodation space in the east during deposition of the Bantimala redeposited facies. In certain areas, palaeoflow towards the east and the overlap of redeposited facies from the two source areas in the northern palaeocurrent grouping imply a surface sloping towards the east. If this inferred eastward palaeotilt existed, slopes would have been very low since the two northern palaeocurrent groupings indicate that palaeoflow was mainly north directed.

Morphology of the faulted margin Two configurations of the faulted northern area are feasible from the late Eocene onwards. The first is domino style faulting, with the Barru Block being downthrown relative to the Bantimala Block. The second scenario is an east-dipping relay ramp between two major parallel faults; the north- bounding faults to the Barru and Bantimala blocks.

An east-dipping relay ramp between two major parallel faults is the preferred configuration of the northern area for the reasons outlined below and illustrated in Fig. 11.

(a) The abundance of low energy marl facies east of the north-bounding fault to the Barru Block suggests that the Barru Block was not undergoing erosion and did not have topographic relief east of its present day outcrop. The general lack of coarse redeposited facies north of the easternmost outcrop of the Barru Block suggests the north-bounding fault to the Barru Block did not continue south- eastwards. The Camba Formation is not displaced east of the Barru Block, which also suggests the block bounding fault dies out towards the SE.

(b) Much of the palaeocurrent data from redeposited facies in the two northern palaeocurrent groupings is north-directed. This indicates that sedimentation rates were high enough to overcome the dip slope of the hanging wall block. Lower angles of dip on the hanging wall block would be expected in the relay ramp situation. In the domino fault model axial flow between the two major faults towards the east, the direction of regional tilt, would be more likely. The Bantimala redeposited facies were transported slightly further north than the northern margin of the Barru Block. This

Horizontal scale / 0 5 10 .

km ' ..-/"" Vedical exaggeration /

~ " / " /

: "'" Block

i ; Barru Block ~ ,

', , ~" , •", ," ~.' ....... :::::::::::::::::::::::::::::::::::::::::::::: .

-- • .,. ,,.

Key ~ [ ] Basinal marl ~_~ Redeposited facies

Shallow water platform carbonate Sandstones, shale and coal

~ . " Shales, sandstones and conglomerates I ' .1 Metamorphic, volcanic and sedimentary lithologies

~ Areal extent of the redeposited facies Overlap of redeposited facies

~Z :':':"7 -- Sea,eve, ~'-: : - /~, . Fault and direction i : : : ' 7 ~ of movement . ~ . . ~ Karstification of subaerially

~","" exposed limestone ~ Transpod direction of

redeposited facies

Fig. 11. Block diagram showing the preferred reconstruction of the northern margin of the Tonasa Carbonate Platform in the Barru area during the late Eocene. Two tectonically active, major NW-SE trending normal faults are separated by an east-dipping relay ramp. The area is thought to have been tilted gently towards the east.



380 M.E.J . WILSON • D. W. J. BOSENCE

situation would be most unlikely in a domino fault block model.

(c) With domino style faulting and tilting, footwall exposure of both major faults might be expected. In the relay ramp situation the two main faults border different parts of the same large block. With tilting of a large single block, the northern Ban'u Block area would have been more likely to undergo emergence compared with the more southerly area of the fault bounding the Bantimala Block. Earlier subaerial exposure of the Barru Basement area did occur, suggesting a relay ramp model is more appropriate (Fig. 11).

The lack of a SE continuation of the north- bounding fault to the Barru Block, redeposited facies distribution, and patterns and timing of sub- aerial exposure of footwall areas all suggest that a relay ramp is the more appropriate configuration for the platform margin.

History of the platform margin Changes in the bed-thickness, clast-type and content of the redeposited facies through time can be used to constrain the history of the platform margin (cf. Everts 1991; Reijmer et al. 1991). Figure 12 is a plot of the bed thicknesses of the redeposited facies against the percentage of clast types and ages, based on point counting thin sections. The plots on the right hand side of Fig. 12 highlight the percentage of clasts older than the background marl sedimentation and the percentage of clasts which are lithic fragments.

Ages for the background marl sedimentation are derived from nannofossil (E. Finch pers. comm. 1993) and planktonic foraminifera identification (T. Wonders pers comm. 1992; E Banner pers. comm. 1994). Provenance studies and a knowledge of the stratigraphic sequence in South Sulawesi can be used to infer an age for non-carbonate clasts. For example, metamorphic and quartzose sandstone lithologies could only have been derived from pre-upper Cretaceous and upper Cretaceous- Eocene non-carbonate formations respectively (Fig. 10b). Although it may be possible to date limestone clasts containing large benthic foraminifera (cf. Adams 1970), many of the carbonate grains cannot be dated. The presence of Discocyclina, Pellatispira or Biplanispira indicates Eocene ages, whilst Lepidocyclina indicates an Oligocene or younger age. Unbroken delicate planktonic foraminifera or rip-up marl clasts are considered to be contemporaneous with the background basinal marl sedimentation. Clasts of planktonic foraminifera bioclastic packstones occur very rarely.

Redeposited carbonate units are thickest during three periods of time: late Eocene to early

Oligocene; latest early-early late Oligocene and early to middle Miocene (Fig. 12). When the redeposited facies are thickest, thick-bedded, clast- supported breccias are the dominant facies and marls occur rarely. During these times between 40- 90% of grains or clasts are lithic fragments and correspondingly a significant proportion of the clasts are older than the background marl sedimentation. In comparison, when the redeposited facies beds are thinner, marls are more abundant, there is a decrease in the amount of lithic clasts, and the majority of clasts are contemporaneous with the background sedimentation (Fig. 12).

It has been inferred above that the main cause of the redeposited facies was tectonic activity on a faulted carbonate platform margin. Derivation of lithic clasts and lithologies older than contemporaneous marl sedimentation would have occurred during periods of faulting. At these times the footwall block would have had relative relief leading to 'exposure' and erosion of the block margins. Earlier lithified material from these elevated areas was prone to reworking into hangingwall depo- centre areas. Since karstification of the Bantimala footwall area is only inferred from the late Oligocene, it is important to note that for much of the time erosion probably occurred in a sub-marine rather than a sub-aerial realm. Submarine down- slope redeposition of shallow-water carbonate material is common along the margins of many modern carbonate banks due to slope instabilities (James & Ginsburg 1979; Mullins 1983). Three main phases of tectonic activity on the platform margin are inferred. These occurred during the late Eocene to early Oligocene, latest early/early late Oligocene and the early to middle Miocene (Fig. 12). These three phases can now be compared with more regional tectonic events.

Regional comparison The Tertiary sequence in the western part of South Sulawesi is similar to sequences in neighbouring Kalimantan and the east Java Sea. It has been postulated that the whole region was part of a widespread basin; the formation of which commenced in the early-middle Eocene (Daly et al. 1987, 1991; Pieters et al. 1987; Van de Weerd & Armin 1992). The Eocene was a period of widespread plate reorganization in SE Asia during which India collided with Eurasia (Dewey 1980; Patriat & Achache 1984; Daly et al. 1987, 1991). The bend in the Hawaii-Emperor sea mount chain also developed at this time, indicating a possible change in the motion of the Pacific plate (Daly et al. 1987, 1991). The Australian-Eurasian spreading centre shifted to its present southeast Indian location, during the Eocene (Packham 1990). Although this




1100

1000

900

Thickness of redeposited

, , , , , , , , ,

~ I ~ "~ ~ carbonate units (m) 1 2 3 4 5 1 0 1 5 2 0 2 5

~f--'~, NN2-NN6 early/middle _ I1 - - \ Miocene

PN6-N7 middle Miocene

early Miocene

800

NP23 latest early/early late

Oligocene

~.~ NP23 latest early/early late Oligocene

~'Ca rf:16n-at-e ~ rac ies - t y l~s . . . . . 700 / ~ = BP - Bioclastic packstone

/ ~ ~ MSB- Marl supported breccia • I CSB - Clast supported breccm

GBP - Graded b oc ast c packstone \ ~ PFW - Planktonic foraminifera i \ wackestone

-_ A_r k_os_i c packs t _one _ J

i " ~ . . . .

" ! _ Early Oligocene

600 i i _~.~_[ _carbonate facies ~ - - ' ~ / ' ~ E n v e l o p e of bed - ~' thickness of the

_ ---- ~ redeposited

I ~ ~ NP18-NP20 late Eocene R

500 =...___)1=17 late Eocene

470 ~ ") D 0 n n ~ E ] 1 2 3 4 5 1 0 1 5 2 0 2 5

~ o ~ Thickness of redeposited Carbonate facies carbonate units (m)

0 %

\ 'Envelope' " showing trend \ of increasing

\.~-___ percentage of \ clasts older \ than - background • , marl \ sedimentation.

!:_-_-_-_:-~ • ..,

" 1 / " 1

i ..

~ ~2,v,¢>.~ x.~.~ =¢ J52

~ J30 ~ J28

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~ =lcwI 062

% Clast age Sample % Clast type 100 No. 0 % 100

J106 t ' ~ , , ' , , ' , .'_- ,'., ,'., , ' , J !

'Envelope' i ,. showing trend \ of increased

percentage of i li~ic fragments.i

=

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D79

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i D28 . k -=_;=_;=_;=_;=_; , j , '_ - . : - ._ , . - . . . -= ! D25 I . . . . ~ ; ~ " ,." ~ 11 D 2 3 ".= : - " -'.-'_" -~:. r-.'.-r.;~ C •

\ . \

D2 ' h = : - = : - = ; - = ; - = : - = ; - = - ~ _ : . , : . , J i

DR23 ~ - - . - " = - - . , ' : ' ; . • " . . ". • ". • ". • i

J an36 k-.,-_ . . . . . :_.:':.,"_'U-.-.,i F ~,e-,re?; . . . . . . . . . . . . . . . . . . ',',-&e-, ; ~ . . . . . . I mini Pre late Cretaceous [ ] Miocene carbonate ,, F~ Lithic clas '~,~ i [r~ ?Palaeocene/Eocene r - I Undated carbonate ii ~ . . . . t ~ I.--I UlOClaSIs - sandstone ~ . - - ma Contemporaneous iI fraomented = [ ] Eocene carbonate m basinal sediments H r~ _. ° . . . . I h n n V I I 1151oclasIs WhOle [ ] O "goce e carbo ate [ ] olcanic casts == i j r .

Fig. 12. Point-counting data plotted against the bed thicknesses for the redeposited facies in the Rala measured section. Note the increased percentage of clasts derived from earlier formations or reworked from older shallow marine carbonates of the Tonasa Limestone Formation when the redeposited beds are thickest.



382 M . E . J . WILSON & D. W. J. BOSENCE

plate reorganization is thought to have resulted in Eocene basin formation, in detail the mechanics of this basin formation are as yet unclear. Initiation and formation of different parts of the basin have variously been related to extensional back-arc formation (Hamilton 1979; Daly et al. 1987, 1991) and a foreland-fore-arc flexural origin (Williams et al. 1988; Hutchison 1989).

Two major fault trends are apparent from seismic data in the Makassar Strait offshore Sulawesi (Fig. 13). Approximately NE-SW trending faults have been related to back-arc extension due to roll-back of a plate subducting eastwards under eastern Sulawesi (Daly et al. 1987, 1991; Letouzey et al. 1990). Although Eocene-Oligocene volcanics in eastern South Sulawesi are thought to delimit the plate margin, detailed analysis has not been under- taken and it is not clear if these volcanics are related to subduction (Letouzey et al. 1990; Van de Weerd & Armin 1992). In the Kalosi area upper Miocene-Pliocene igneous rocks have been related to subduction of continental crust (Bergman et al. 1996). Another possibility is that the Makassar Strait extension may represent a failed arm- extremity of sea floor spreading in the Celebes Sea to the northeast (Hutchison 1988; Moss 1994). The second group of faults trends NW-SE and includes the Adang and Sangkulurang faults (Fig. 13).

NW TT-2 TT-1 SE

1 ~ - ~ : - - ~ I ~ ~ z , ~ "-~r-__-S,-_z '% t

km ~ 4

TT-1 m 0 mid-Miocene to Recent 192

m TT-2

62 early to mid- i KEY 82 1 . ~ Mi°cene i [ ] Deep marine

" , shales + marls 1238 . . . . . . . Redeposited :: ,,mestonetaces

1 5 ~ ~ Shallow marine

\\ ~ '~ ] ~ marine elastics(Marginal). , rq~,~, Oligocene ~ "~, ~ 2182 to early ~ Non marine

\ ~ i~~ Miocene ~ clastics

~\ \\. ~ ] ~ Basement ', ,\ ~ . . . . . . . . . . . . . . . . . . .

~ 2892 . . . . . . . . . . ~. ~ 3055 Eocene ~ ~ 3238 ~ J , ~ i no recovery

3560 . . . . . . . . . . ]~P'--7] Cretaceous-inferred

Fig. 14. Seismic section and borehole data from the inverted Taku Talu fault, Makassar Straits (after Situmorang 1987). See Fig. 13 for location of boreholes.

~ Outcropping Eocene to Holocene .TT-2 Borehole location (see Fig. 14) [ sedimentary basin fill pre-Cretaceous continental crust ..-,.-- j SubductionFaUlt - tick markSzone downthrow side

Fig. 13. Map to show the location of Tertiary basins in Kalimantan and western Sulawesi. Modified after Van de Weerd & Armin (1992).

Offshore analogue o f the northern

faul ted margin

The late Eocene to middle Miocene redeposited carbonate facies in the Barru area are inferred to have been derived from the faulted northern margin of the Tonasa Carbonate Platform. An analogous example of syn-tectonic carbonate sedimentation is revealed from seismic and borehole data in the Makassar Straits, from the vicinity of the NE-SW trending Taku Talu fault (Fig. 14). Eocene to middle Miocene carbonate breccias containing clasts from the underlying basement were deposited as a thickened hanging wall sequence, whilst shallow-water carbonate sedimentation continued on the footwall block of the Taku Talu fault (Fig. 14). Thus the Taku Talu fault was a major active Eocene to early Miocene normal fault which underwent later inversion during the middle Miocene (Situmorang 1987).

Adang faul t

The Adang fault is a major NW-SE trending structure separating the North and South Makassar Basins (Fig. 13). This lineament is thought to extend westwards onshore forming the southern




boundary of the Kuta Basin and has been linked across Borneo with the Lupar Line forming a 'trans-Borneo shear' (Woods 1985; Kusuma & Darin 1989; Wain & Berod 1989; Bransden & Matthews 1992; Van de Weerd & Armin 1992). Both strike-slip (Woods 1985; Hutchison 1989; Biantoro et al. 1992) and normal displacements (Biantoro et al. 1992; Rangin et al. 1990) on the Adang fault have been inferred. It has been suggested that the Adang fault was an important Eocene to early Miocene normal fault downthrowing to the north, which subsequently underwent strike-slip reactivation during the middle-late Miocene (Kusuma & Darin 1989; Rangin et al. 1990; Biantoro et al. 1992). During the late Eocene to Miocene the Adang fault had a strong influence on sedimentation patterns. The Paternoster Platform and Barito Basin were the sites of shallow-water carbonate development, whilst deeper sedimentation occurred in the Kuta Basin to the north (Van de Weerd et al. 1987; Kusuma & Darin 1989; Wain & Berod 1989).

Seismic data across the Makassar Straits (D. Coffield pers. comm. 1995) suggest there was no fault linkage between the NW-SE trending Adang Fault and the main north-bounding fault to the Tonasa Carbonate Platform. It is suggested that NW-SE trending structures influenced sedimentation patterns in Sulawesi and Kalimantan. NNE- SSE trending faults such as the Walanae Fault also had an effect on Tertiary sedimentation patterns in western Sulawesi (Van Leeuwen 1981; D. Coffield pers. comm. 1995). Seismic data N-S across the Sengkang Basin reveal normal block-faulting, with blocks being downthrown to the centre of the basin (A. Ngakan pers. comm. 1994). Indeed, the north- bounding faults to the Tonasa Carbonate Platform and faults with a similar trend to the east may mark the southern boundary of the NW-SE trending depression, which runs through the Sengkang Basin and appears structurally to separate South Sulawesi from the rest of the western arc of Sulawesi (Fig. 1).

Timing

Redeposited carbonate facies in the Barru area suggest three phases of tectonic activity in the area during the late Eocene-early Oligocene, early- late Oligocene and early-middle Miocene. Other evidence for possible tectonic activity in the region is documented below and possible causes are discussed (Fig. 15).

Ear ly -mid Eocene. A basal angular unconformity to many initially transgressive Tertiary sequences marks widespread basin initiation (Cater 1981; Pieters et al. 1987; Van de Weerd et al. 1987;

Kusuma & Darin 1989; Wain & Berod 1989; Letouzey et al. 1990; Bransden & Matthews 1992; Hutchison 1992; Van de Weerd & Armin 1992). The angular unconformity between the Malawa Formation and underlying Balangbaru Formation is one such contact. Basin initiation possibly occurred as early as the Palaeocene in some localities (Bishop 1980; Cater 1981; Wain & Berod 1989). Carbonate production, including the deposition of the Tonasa Limestone Formation, had begun in many areas by the middle to late Eocene. Active faulting and graben formation has been inferred from seismic (van de Weerd et al. 1987; Bransden & Matthews 1992) and outcrop data (Tyrrel et al. 1986; Kusuma & Darin 1989). Basin formation is thought to be a response to widespread Eocene plate reorganisation.

Late Eocene-ear ly Oligocene. This period corre- sponds with the first phase of coarse redeposited facies in the Barru area, indicating the initiation (or reactivation) of faulting on the margin of the Tonasa Carbonate Platform. The geometry and timing on major faults from regional seismic data suggest that localized extension was underway by the early Eocene (P9/P10), and rifting was widespread by the late Eocene (Van de Weerd et al. 1987; Letouzey et al. 1990; Bransden & Matthews 1992). The major variation in preserved thicknesses across faults, and hence syn-tectonic deposition is observed during the late Eocene and early Oligocene (Bishop 1980; Bransden & Matthews 1992). During the late Eocene a significant tectonic event caused widespread high angle faulting and subsequent erosional truncation affecting a number of areas (Bransden & Matthews 1992). This period is thought to represent the main extensional phase in the region (Letouzey et al. 1990; Bransden & Matthews 1992). The middle- late Eocene is also the age of the oldest oceanic crust in the Celebes Sea (Weissel 1980).

Middle Oligocene. A mid-Oligocene unconformity has been reported from many offshore (Bransden & Matthews 1992) and onshore areas (Van Leeuwen 1981; Kusuma & Darin 1989; Van de Weerd & Armin 1992). This unconformity, the major shift in facies belts, localized channelling and thickness variations have been related both to the mid Oligocene eustatic lowstand (Bransden & Matthews 1992) and tectonic activity (Cater 1981; Van de Weerd et al. 1987; Wain & Berod 1989; Sailer et al. 1992; Van de Weerd & Armin 1992). Sailer et al. (1992) reported exposure and subsequent deepening prior to the middle Oligocene (29.5-30 Ma) sea-level fall of Haq et al. (1987). In Sulawesi the second phase of coarse redeposited facies in the Barru area, an unconformity in the



384 M.E.J. WILSON (~ D. W. J. BOSENCE

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Fig. 15. Tertiary stratigraphic correlation chart, showing similarities between the sequences in Kalimantan, East Java Sea and Sulawesi. Data taken from Bishop (1980), Cater (1981), Van de Weerd et al. (1987), Kusuma & Darin (1989), Wain & Berod (1989), Bransden & Matthews (1992) and Van de Weerd & Armin (1992).

Biru area (Van Leeuwen 1981) and minor localized evidence for exposure on the Tonasa Carbonate Platform (personal observation) during the mid Oligocene, all suggest a tectonic cause. During the Oligocene sea floor spreading began in the South China Sea (Holloway 1982; Ru & Pigott 1986; Daly et al. 1991) and the east Sulawesi ophiolite was emplaced (Parkinson 1991).

Early to middle Miocene. In the Barru area west- verging folding affects both the Tonasa Limestone Formation and the overlying middle-late Miocene volcaniclastics. The latest Oligocene to middle Miocene phase of the Bantimala Redeposited Facies therefore records a period of faulting and uplift prior to folding (and possible inversion). Based on seismic evidence from the east Java Sea and Makassar Strait, contemporaneous faulting and syn-tectonic graben fills have been inferred until the early Miocene (Bishop 1980; Cater 1981, Letouzey et al. 1990). Inversion of many of the earlier faults with normal displacement occurred slightly later during the early to middle Miocene (Fig. 14; Letouzey et al. 1990; Bransden & Matthews 1992). This compressive regime, active

up to the present-day, is widely attributed to the collision of microcontinental fragments onto eastern Sulawesi during the middle to late Miocene (Daly et al. 1987, 1991; Van de Weerd & Armin 1992). The middle to late Miocene is also the time when a volcanic arc developed in western Sulawesi (Sukamto 1975; Yuwono et al. 1985; Coffield et al. 1993; Bergman et al. 1996).

Similar to the major bounding faults of the north margin of the Tonasa Carbonate Platform, many of the faults mentioned above had major normal displacements. Inferring an additional strike-slip motion would depend on along-strike linkage of faults, a factor which is difficult to ascertain from the available seismic and outcrop information. A transtensional Palaeogene history for the region has been suggested on the basis of the length of faults, apparent reversal and observed variability of fault trends (Bishop 1980; Bransden & Matthews 1992).

C o n c l u s i o n s

Late Eocene to middle Miocene redeposited facies of the Tonasa Limestone Formation in the Barn]




area provide a unique example of the use of carbonate sedimentology in comparing local and regional tectonic events. In the shal low-water carbonates of the Tonasa Carbonate Platform to the south, tectonic effects are impossible to distinguish from eustatic effects. However, clast composi t ion and facies types in the redeposited carbonates reveal that tectonic and not eustatic changes were the main controls on sedimentation. In fact, redeposited carbonates in the Barru area prove to be a remarkable natural seismograph, recording regional tectonic changes and a number of local and regional conclusions can be inferred from them.

(1) The spatial distribution, basement clast content and prox imal -d i s ta l trends within redeposited facies suggest derivation from two main source areas. These areas were from the northern margins of the Bantimala and Barru Blocks.

(2) The textural immaturi ty and provenance of clasts indicate that the redeposited facies were derived from the faulted margins of a carbonate platform. Redeposited facies were derived from at least two faulted line-sources and were deposited as sheet flows forming carbonate aprons at the base of the slope.

(3) An east-dipping relay ramp between two main N W - S E trending faults is the preferred configuration of the northern margin of the Tonasa Carbonate Platform.

(4) The redeposited facies indicate three phases of tectonic activity. These occurred during the late

Eocene to early Oligocene, the middle Oligocene and the early to middle Miocene. This is consistent with other similar sequences in Kalimantan and the East Java Sea and with inferred regional plate tectonic changes.

(5) The northern faulted margin of the Tonasa Carbonate Platform has a similar trend to N W - S E orientated structures in the Makassar Straits and Kalimantan. These structures are inferred to have inf luenced sedimenta t ion patterns dur ing the Eocene to middle Miocene.

The senior author gratefully acknowledges BP Exploration, UK for their generous financial support during the course of her PhD study, of which this work forms a part. The SE Asia Research Group, Royal Holloway, University of London, especially Dr Tony Barber and Diane Cameron, are thanked for their administrative and technical support. In Indonesia, Alexander Limbong, the senior author's counterpart from GRDC, Bandung, during three gruelling 'non-stop' field seasons deserves special thanks. GRDC, Bandung, Kanwil, South Sulawesi, particularly Darwis Falah and family, BP offices in Jakarta and Ujung Pandang and LIPI all provided technical and practical support. Dr Ted Finch and Prof. Fred Banner at University College London, and Dr Toine Wonders, Consultant, UK, are thanked for their excellent biostratigraphic work. The constructive comments from referees Dr Dana Coffield and Dr Neil Harbury and those by Dr Tony Barber, Rob Bond, Nigel Deeks and Dr Steve Moss towards improving this paper were much appreciated. Keith Denyer is thanked for producing the photographic plates.

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