Sulawesi Geological Society, London, Special Publications

Geological Society, London, Special Publications

Sulawesi

Michael Geoffrey Audley-Charles

Geological Society, London, Special Publications 1974; v. 4; p. 365-378 doi:10.1144/GSL.SP.2005.004.01.21

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1. THE SEGMENT STUDIED The island of Sulawesi--formerly called Celebes--occupies a critical SULAWESI but very complex position at the junction of the Alpine-Himalayan and Circum-Pacific chains. It links along strike with both the Philippine and the Banda orogens, but lies between the Borneo and the West MICHAEL GEOFFREY AUDLEY-CHARLES Irian orogens. The island is one of the most mountainous in the Department of Geology, Imperial College, Indonesian Archipelago and is poorly known geologically, because of Prince Consort Road, London S.W.7 which the present article is largely in essay form. Segment: the Sulawesi orogen has a strike length, excluding small Islands, of about 1300 km. The west margin of the belt consists of an arc CONTENTS open in the south to the south-east, which reverses its direction of curvature in the north to form an arc open to the north-west. In the A. General data on the segment 365 south it is separated from the Sunda Shelf by the 2000 m deep B. Subdivision of the segment 374 Makassar Strait and in the north it is adjacent to the Celebes Sea. C. Structural relationships of the The east margin of the belt abuts against the Banggai and Sula Islands (part of a stable positive area called the Sula Spur) and, to Sulawesi Arcs with neighbouring regions 376 the south, against the northern part of the Banda Sea. The width D. References 377 of the orogenic belt in Sulawesi, measured between these margins, varies from 500 km to 270 km, and averages 350 km. History: the oldest rocks known in Sulawesi are sedimentary rocks which have been metamorphosed in pre-U. Triassic times. Then, there seems to have been a period of general uplift and erosion in Sulawesi. Mesozoic-Cenozoic orogenic movements commenced during U. Jurassic and L. Cretaceous times with vertical movements, perhaps associated with some folding, in the Butung Archipelago and the South-east and South Arms of Sulawesi. It is possible there were fold movements at the end of the Triassic in the west of Central Sulawesi and in parts of the East Arm, but palaeontological control is un- satisfactory and the rocks have been mapped on a reconnaissance basis only. The first phase of strong folding began at the end of the Cretaceous and was completed during the L. Eocene in most parts of Sulawesi and in the Butung Archipelago (Bemmelen 1949). A major phase of folding and thrusting of M. Miocene age is reported from the East Arm, and may also have occurred in Central Sulawesi and the North Arm. An important phase of folding (locally with overthrusting) during the late Pliocene is reported throughout Sulawesi and the Butung Archipelago. The stratigraphy and structure of Sulawesi are poorly known, for the density of reconnaissance geological mapping in the island is low. All published geological maps appear to be based on surveys carried out before 1942 (see Roy 1961 ; Tectonic Map of Eurasia 1966; U.S.G.S. 1965). Few topographical maps were available; aerial photography was not then employed so that many of the published maps show only the geology of the immediate vicinity of the traverses. Only three papers dealing with regional geology of parts of Sulawesi 366 SULAWESI

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Figure 1. The structural zones of the Sulawesi orogenic belt, their correlation with those of the Banda Arcs orogenic belt, and their relationship with the Sula Spur (shown by coarse dotted ornament). SULAWESI 367 appear to have been published since Van Bemmelen's The Geology of the western part of the Salajar-Lucipara Arc) curves through 270 ° Indonesia of 1949. A further impediment to understanding the structural and has a strike length of 1900 km, or of 1300 km if those arcs of small history is the often uncertain age of sedimentary, igneous and meta- islands are omitted. The lengths of radii of curvature of the principal morphic rocks. Many of the published ages of the Cenozoic strata are arcs are 500 km for the 'outer' arcs (East Celebes and Tukangbesi Arcs). based on foraminifera determined before 1948 and names are In the north the curvature of the arcs is reversed: the radius of the probably in need of revision to bring them into line with recent work. 'inner' North Celebes Arc is 400 km and that of the 'outer' North Each of the four arms of Sulawesi appears to have a different Moluccan Arc is 550 km. geological history, but it has long been recognized that the North Arm, the western part of the Central region and the South Arm have fundamental features in common which distinguish them from the 3. SURFACE SHAPE OF THE SULAWESI BELT South-east and East Arms. IN ELEVATION The present article has been prepared from a literature review: 30 Highest 5% of the ground: 2000 to 2500 m above sea level. Sulawesi the writer has not visited Sulawesi. is one of the most mountainous islands of the Indonesian Archipelago. Most of the highest land is in Central Sulawesi, but all the arms are 2. SHAPE OF THE OROGEN IN PLAN mountainous and nearly 40% of the land area is over 500 m above sea 33 The Sulawesi orogenic belt (including the North Celebes Arc and level. 33-4 Plio-Pleistocene raised reef limestones have been reported from the East Arm at various heights. Bemmelen (1949, p. 151) quoted heights of 400 m, 500 m, 1000 m, and possibly even 2000 m in the western part of the East Arm (cf. Loczy 1934). An old alluvial surface 20 to 30 m above the present one occurs on the north coast of the East Arm and indicates minor subrecent uplift (Koolhoven 1930, p. 207). \FS

4. GEOPHYSICAL DATA BORNEO 38 Gravity data are available as a map on a scale of 1:10,000,000 with a 50 mgl contour interval for the marine areas surrounding Sulawesi (Kuenen, Umbgrove & Vening Meinesz 1934). A revised isogam map

"*~"*" ~ e'. e e" • e" • " j • " • • lee e' t. for the whole of Indonesia has since been published (Bruyn 1951). oe4 • o°o • e°e e • • • • • • It incorporates the gravity data of Vening Meinesz and data from land based surveys, is on a scale of 1:10,000,000 and has a contour interval of 25 mgl. 41 There is isostatic inequilibrium over most of Sulawesi and this is greatest in the East Celebes and North lV[oluccan Arcs. 42-3 As far as can be judged from available data the general gravity field shows pronounced concordance with the main tectonic and topographic trends of Sulawesi. There are several outstanding features of the gravity field: very TIMOR strong negative values are coincident with the marine section of the North Moluccan Arc; strong positive values coincide with some i NN,-.'b %-~ deeper parts of the surrounding seas, e.g. Celebes Sea and Banda Sea; Figure 2. The distribution of the arcs of the Sulawesi orogenic belt and Banda Arcst strong positive anomalies are coincident with the marine gulfs which orogenic belt. l=Outer Sunda Arc; 2=Inner Sunda Arc; 3=Outer Banda Arc; separate the inner and outer arcs of Sulawesi and the outer arc from 4 = Inner Banda Arc; 5 = Tukang Besi-Buru Arc; 6 = Salajar-Lucipara Arc; 7 = East Borneo. Bruyn (1951, p. 605) remarked that 'It is certainly possible to Gelebes Arc; 8 = Western Celebes Arc; 9 = North Moluccan Arc; 10 = North Celebes recognize on the profiles across Sulawesi the characteristics of a double Arc; 11 = Halmahera Arcs. S = Sorong Fault Zone; TA = Tarera-Aidoena Fault Zone; T = Tawaelia Fault Zone; FS = Fossa Sarasina. arc. Here (i.e. all Sulawesi except the Minahasa section of the North The area of coarse dotted ornament represents the Sula Spur. Arm), however, the curvature is reversed so that the Vening Meinesz 368 SULAWESI minimum is found on the concave side of the arc. No active volcanoes Sulawesi and the archipelagos to the north and south Pliocene rocks are present (in the section of reversed curvature). The high positive have been folded. Palaeontological evidence is not sufficiently precise values coinciding with the deep water of the Makassar Strait are to be certain that these movements did not continue into the Pleistocene comparable with those of the Banda Sea. As soon as the curvature (see Bemmelen 1949, pp. 149-52, 389-436; Vlerk & Dozy 1934). returns to normal (i.e. the minimum on the convex side of the arc) Before the age of the tectonic events in the Cenozoic rocks of Sulawesi active volcanoes reappear, namely Una-Una and those on the North can be correlated reliably with those in other Cenozoic fold belts the Arm of Sulawesi and the Sangihe Islands. Here the profiles show the faunas need to be reviewed in the light of the biostratigraphy of Blow standard sequence of maximum and minimum axes, troughs and (1969). ridges.' 9t-5 Phases of mobility 10. Plio-Pleistocene uplift: Geomorphological evidence for this event has been reported from all parts of Sulawesi. The process 5. PRESENT-DAY ACTIVITY is probably still continuing. 69 The Sulawesi region is seismically active, and the northern half is 9. Late Pliocene phase: This was important and widespread. An very active. Gutenberg & Richter (1954, pp. 60-61) commented that unconformity with gentle folds occurs in the East Arm (Kundig seismic activity in the Celebes 'is well above average for the Pacific 1956; Loczy 1933-4; Umbgrove 1938; Bemmelen 1949), in the belt; intermediate shocks are very numerous and some of them South Arm (Umbgrove 1938), in Central Sulawesi (Witkamp (notably in northern Celebes) are among the largest known. Deep 1940; Vlerk & Dozy 1934), and in the South-east Arm (Umbgrove shocks are fairly frequent.' Fitch & Molnar (1970) remarked that 1938; Bothe 1927). In the Butung Archipelago Bothe (1927) and 'The occurrence of earthquakes between 300 and 500 km depths in Hetzel (1936) reported strong folding and thrusting of Pliocene the Banda Sea region is an indication that the lithosphere is continuous age. The evidence for the age of these tectonic events rests mainly there. This activity may be a consequence of the marked contortion on the foraminifera determined at that time. It seems likely that in the seismic zone.' The difficulty of interpreting important features the age of the folding would still be regarded as Pliocene, but in of the seismic behaviour of Sulawesi and the Banda Arcs in terms of view of the anomalous directions of movement, the faunas might regional tectonics was pointed out by Fitch & Molnar: 'A zone of profitably be reviewed in the light of Blow's (1969) work. The intense intermediate-depth activity paralleling the northern peninsula movements might range into the Quaternary. of Celebes forms the southern terminus of the deep-focus activity 8. Middle Miocene phase: In the East Arm this is the major beneath the Philippine arc. There are similarities between the con- orogenic phase (Kundig 1956) and involved strong folding and figuration of this zone and the seismic zone beneath the Banda Sea. thrusting. The presence of an unconformity between U. and L. Both regions have intense activity extending from the surface nearly Miocene, which may represent M. Miocene uplift, erosion and vertically to approximately 200 km. Below 200 km activity is less, possible folding, was reported from the Gorontalo and Minahasa and it is along a plane which dips approximately 45 ° beneath the sections of the North Arm (Koperberg 1929-30; Bemmelen respective arcs.' 'East of the Celebes Sea is a complicated seismic 1949). An unconformity between the Oligo-Miocene and the region associated with an island arc paralleling the northern peninsula 'Celebes Molasse', which Umbgrove (1938) regarded as a M. of Halmahera. A cross section of the activity in this region shows that Miocene Tf2 unconformity, was reported from Central Sulawesi the zone beneath the Celebes Sea dips towards the west while another by Witkamp (1940) and may possibly represent an orogenic zone extending only to intermediate depth dips towards the south-east. phase there. The report of a transgression in the 'post-Tertiary-f' This eastward-dipping zone is very unusual, and its relation to the (i.e.M. Miocene) in the South-east Arm by Bothe (1927) may be tectonics of the region is not apparent to us.' More recently, further related to M. Miocene or possibly U. Miocene movements. maps of the seismic epicentres have been published (Fitch 1970). Local erosion in M. Miocene time in the Butung Archipelago was Hatherton & Dickinson (1969) figured seismic isobaths to the north, reported by Bothe (1927). south and east of Sulawesi. 7. Lower Miocene: An unconformity at the base of the Miocene Tondo Beds was reported from Butung (Hetzel 1936; Bothe 1927). Umbgrove (1938) reported an unconformity of L. Miocene 6. TIME RELATIONS (Te4) age from Central Sulawesi and the East Arm, but Kundig (1956) made no mention of this unconformity in the East Arm. 85 The oldest undeformed rocks in Sulawesi are of Quaternary age. They 6. Oligocene: An unconformity at the base of the Oligocene is are mainly raised reef limestones, alluvium and coastal plain deposits, reported from Central Sulawesi (Bemmelen 1949). In the northern many of which are highly fossiliferous. part of the South Arm the main phase of folding and thrusting is 83 The youngest deformed rocks are late Pliocene in age. Throughout said to occur in the Oligocene (Rutten 1927; Bemmelen 1949). SULAWESI 369

An unconformity at the base of the L. Miocene Tondo Beds of island of Kabaena evidence suggests there was an important Butung (Bothe 1927) may represent Oligocene movements. The phase of metamorphism (glaucophane facies) penecontemporane- uncertainty results from the lack of a sufficiently diagnostic ous with these end-Cretaceous orogenic movements in the South- microfauna. east Arm (Roever 1950, 1953, 1956). A major unconformity 5. End-Cretaceous to Eocene phase: In the South-east Arm a major between the Cretaceous Tobelo Beds and the L. Miocene Tondo unconformity is present between the Cretaceous and the Neogene Beds is widespread in Butung Archipelago where it is considered (Eocene and Oligocene rocks are missing) and represents a period to have resulted from a period of folding, uplift and erosion of strong folding, uplift and erosion (Bothe 1927; Brouwer et al. (Bothe 1927; Hetzel 1936). The local occurrence in Butung of the 1934; Hetzel 1936; Bemmelen 1949). Here and in the nearby Wani Beds of either Eocene or Oligocene age, unconformable on but folded with the underlying Cretaceous Tobelo Beds, indicates an important orogenic phase at the end of the Cretaceous,

~__~ I 250km perhaps extending into Eocene or even Oligocene time. In the South Arm an important unconformity between Cretaceous and Eocene strata represents a period of folding and erosion; in the northern part it marks the onset of andesite volcanism (Rutten 1927; Brouwer et al. 1934; Bemmelen 1949). Owing to the lack of precisely diagnostic faunas there is some doubt about the time CELEBES SEA limits of these movements. In the East Arm the actual contact between the Cretaceous and Eocene has not been observed. Kundig (1956) thought it probable that there was a depositional gap between the Cretaceous and the Palaeocene, and that this interval coincided with the main phase of ophiolitic extrusions. The rapid change from abyssal facies in the Cretaceous to nerific facies in the Eocene seems to indicate strong vertical uplift at the end of the Cretaceous in the East Arm. In the western part of Central Sulawesi an important unconformity resulting from fold UNA UNA I$, ~ GORONTALOTROUGH o~::~ movements and erosion separates Cretaceous and basal Tertiary TOMINI strata (which have locally been determined as Eocene) according GULF to Witkamp (1940) and Bemmelen (1949, p. 409). 4. Intra-Cretaceous phase: In part of the South Arm a siliceous o -" "~ facies of probable Cretaceous age is overlain unconformably by a greywacke-sandstone facies that is also thought to be Cretaceous on the basis of its stratigraphical position and analogous litho- NORTHERN logy (Rutten 1927; Brouwer et al. 1934; Bemmelen 1949). If these facies have been correctly identified as Cretaceous there is BANDA SEA evidence for a period of folding and erosion in the southern part of the South Arm during the Cretaceous. 3. Upper Jurassic--Lower Cretaceous phase ?: The Cretaceous Tobelo Beds in Butung are in contact with the U. Jurassic Rumu Beds and with other older Mesozoic formations. It is uncertain oGUNUNGAPI HAKASSAR( whether this has resulted from tectonic complications or from a depositional unconformity at the base of the Cretaceous Tobelo Beds (Hetzel 1936; Bothe 1927; Bemmelen 1949). In the East Arm there is no unconformity between the Jurassic and Cretaceous but Kundig (1956) considered that there must have been a phase of great downwarping during U. Jurassic to L. Cretaceous time, because of the sudden change in facies from neritic Jurassic to Figure 3. Location map for the Sulawesi orogenic belt. K.-Z. = Kolonodale zone. The bathyal Cretaceous. named zones of Central Sulawesi are taken from Van Beramelen (1949). 2. Lower Jurassic phase ?: In the west of the East Arm Loczy 370 SULAWESI

110"E ~,200 Isobaths on approximate centre of dipping seismic zone, in km 0' (after Hatherton & Dickinson 1969)

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volcano400"~--~ ~ ~ ]k Active __ ...... _ Faults and f~~" I o O "iolites postulated submarine ~~ M'"~r~ I ~ Granitic intrusions ~ Sula Spur ~0~~- ~ - I~11 Direction of increasing ~- n- - grade of metamorphism ~ Main Islands

~+~~~) +~...--T ---'~ ~ Direction of thrusting 250kin I II I ! ., I Figure 4. The regional distribution of seismic and gravity features of the Sulawesi and Banda Arcs orogenic belts and their relationship to overthrmting, ophiolites, acid plutonics, and recent volcanism. SULAWESI 371

(1933-4) considered that the Triassic rocks were folded prioI to thus lie outside the Sulawesi orogenic belt. To the west of the Sulawesi the deposition of Jurassic strata. Umbgrove (1935) suggested orogenic belt basement rocks are not known to crop out within 200 km that in the west of Central Sulawesi there was a phase of folding of Sulawesi. after the Triassic, followed by erosion after which marine sedimentation recommenced during the Cretaceous. No rocks of 8. STRUCTURAL RELATIONS definitely Triassic age have been reported from western Sulawesi, however. So although it is possible that there were fold movements m-17 Two major faults have been recognized. The Tawaelia Graben and erosion during the Jurassic in these parts of Sulawesi, it zone (Brouwer 1947) strikes N-S in Central Sulawesi and probably cannot be regarded as proved. extends north along strike to cut the North Arm and southwards 1. Pre-Upper Triassic uplift and erosion appears to have been along the west side of the Bone Gulf, passing just east of Salajar. widespread in Sulawesi and Butung. There may have been The age of commencement of movements along this structure is not associated folding but this has not been established. The evidence known, but it separates zones 2 and 3 and so seems to be an important for these events has been discussed by Bemmelen (1949). feature related to the evolution of the belt. It appears to have in- 87-9 The initiation of mobility associated with the Mesozoic-Cenozoic fluenced the distribution of sedimentary facies on either side since the orogeny could be regarded as the marine transgression near the Cretaceous and it limits the distribution of metamorphic facies. The beginning of the U. Triassic that appears to be a widespread pheno- extent of its movements are unknown, but it appears to have acted as menon in Sulawesi. a graben during Neogene and probably earlier times. Mylonite occurs along part of the fault zone where igneous rocks are present. 81 The oldest rocks deformed for the first time during the Mesozoic-Cenozoic The other major fault--the Fossa Sarasina--also appears to behave orogeny are fossiliferous Upper Triassic strata reported from the as a graben in Sulawesi, where it has formed a fault valley. It appears East Arm by Loczy (1933-4) and Kundig (1956). Loczy (1933-4) to strike NNW into the Makassar Strait. It may be much younger and Kutassy (1934) regarded some rocks in the western part as than the Tawaelia structure, but its age of initiation is uncertain. The Permo-Carboniferous but Hetzel (1935) referred to them as 'very Fossa Sarasina and other faults in Sulawesi have been discussed doubtful Permo-Carboniferous'. In the east of Central Sulawesi, recently by Katili (1970). fossiliferous U. Triassic was reported to be the lowest exposed member of a continuous succession up into the Cretaceous (Umbgrove 1938). Fossiliferous U. Triassic Baito Beds in the South-east Arm and the 9. REVIEW OF OROGENIC DEVELOPMENT Einto Beds in Butung (Bothe 1927) are the oldest rocks deformed for the first time by this orogeny there. 132 GEOPHYSICAL EVIDENCE OF OROGENIC STRUCTURE 78 Basement rocks: Crystalline schists of pre-U. Triassic age have been Fitch (1970) stated that data gathered from shallow focus earth- reported from the south-west of the Gorontalo section of the North quakes from 1961 to 1968 show that thrusting and normal faulting Arm (Koperberg 1929, 1930), from the Neck of the North Arm are the dominant modes of deformation in the Philippines, Sulawesi (Egeler 1947), from the western and eastern parts of Central Sulawesi and Bands orogenic belts. The conclusion reached by Ritsema & (Kundig 1932, Williams 1937; Brouwer 1941; De Roever 1947; Veldkamp (1968) that strike-slip faulting is dominant was based on Bemmelen 1949, fig. 171), from the South-east Arm (Dieckmann & data that Fitch (1970) claimed was inadequate by modern standards. Julius 1925; Koolhoven 1932; Brouwer et al. 1934; Hetzel 1936; Another recent paper is that of Hatherton & Dickinson (1969.) Bemmelen 1949), from Butung (Bothe 1927; Hetzel 1936) and from Mechanism solutions from submarine seismic zones on the convex Kabaena (De Roever 1953). From the South Arm they were described sides of the North Celebes and North Moluccan Arcs show evidence as pre-Cretaceous crystalline schists (Rutten 1927; Brouwer 1934; for underthrusting of lithosphere beneath the island arcs. Fitch stated Bemmelen 1949). The age of these basement rocks has been determined that there 'is no evidence from focal mechanisms supporting the from the unconformable relationship of the unmetamorphosed Meso- existence of underthrusting along the eastern end of the Sunda Arc zoic (U. Trias or locally Cretaceous) on the metamorphic basement. (i.e. the Banda Arcs) even though a well-developed inclined seismic To the east of the Sulawesi orogenic belt very similar basement zone exists beneath the arc in this region . . . the close approach of rocks to those just described have been reported from the Sula Islands the Australian continent may have disrupted the simple under- (pre-Liassic crystalline schists, Brouwer 1921); they are generally thrusting in the region'. Also 'inclined seismic zones beneath the regarded as lateral extensions of the pre-U. Triassic crystalline schists (Bands, North Celebes and North Moluccan) arcs show that activity of the Banggai Islands (Bemmelen 1949; Klompe 1954, 1957; Kundig at deep and intermediate depths is in general confined to narrow 1956). There seems to be strong evidence for regarding, as Klompe slab-like regions of the upper mantle'. He claimed that seismic (1954) did, the Banggai Islands as belonging to the Sula Spur. They evidence from this region and other inclined seismic zones 'supports 372 SULAWESI the hypothesis that slabs of lithosphere constituting lateral inhomo- in parts of the Banda Arc (Timor and Left). Brouwer (1919) thought geneities in the upper mantle beneath island arc structures act as that the crystalline schists in the Lesser Sunda Islands (e.g. Timor) stress guides'. might, at least in part, be Permian in age on the basis of a reported On the basis of shallow focus seismic activity, Fitch (1970) defined gradation between them and fossiliferous rocks in Left. Bemmelen boundaries of plates of lithosphere that differ in detail from the plate (1949) doubted the reality of this gradation and postulated tectonic boundaries proposed by Le Pichon (1968) largely by the introduction wedges to explain their association. The field relations in Left need of the Philippine Sea plate (Fig. 5). Fitch has drawn the tentative re-examination. boundary of the Pacific and Asian plates cutting through the East Syn-orogenic (Triassic-Jurassic) history: L. and M. Triassic strata are not Arm and North Arm of Sulawesi. This interpretation seems unknown in Sulawesi, although their presence was postulated by Loczy satisfactory to the present writer on the basis of the published accounts (1933-4). U. Triassic neritic limestones and shales and a paralic of the geology of these regions. facies occur in zone 4. There may have been a period of erosion in zones 2 and 3 during the U. Triassic. In zone 4 sedimentation from the U. Triassic to the L. Cretaceous seems to have been fairly continuous in shallow marine environments. Relatively gentle fold movements may have occurred locally during this period. Syn-orogenic (Cretaceous) history: During the Cretaceous there must have been considerable downwarping of zone 4 for the facies change rapidly from neritic to bathyal, suggesting a correlation with the development of the Outer Banda Arc. In zone 2 Cretaceous deposits appear to belong to two very different facies; one is neritic-paralic, the other bathyal and similar to that of zone 4. It is possible that tectonic dislocations, presently unrecognized, may account for this anomalous association. Alternatively, the east and north of zone 2 may have been downwarped to provide a bathyal environment similar to zone 4, whilst the west of zone 2 remained close to sea level producing neritic sedimentation. Another possibility is that the bathyal environment has been mis-identified. Perhaps the calcilutites and siliceous deposits were laid down in a quiet sea of moderate depth in which little terrigenous sediment entered, so that deposits similar to bathyal facies were produced. Figure 5. Plates of lithosphere within the Sulawesi and Banda Arcs orogenic belts (from Syn-orogenic (late Cretaceous-L. Eocene) history: At the end of the Fitch 1970). Plate boundaries are defined here by shallow focus seismic activity, Cretaceous and possibly extending into Eocene times, there was a shown by the solid curve and by a peeked line where the boundary is poorly defined. major orogenic phase which resulted in folding and local overthrusting. It has been identified in zones 2, 3 and 4, although its effects appear to vary greatly along the strike of the zone, e.g. it appears not to have had much influence, beyond possible uplift, in the East Arm 134 THE OVERALL EVOLUTION OF THE SULAWESl OROGENIC BELT (zone 4). Accompanying this orogenic phase was a major ophiolite Pre-Upper Triassic history: The oldest rocks in Sulawesi are pre-U. eruption in zone 4. Greenschist metamorphism probably occurred Triassic crystalline schists with intrusives. The schists have been during this time in zones 2, 3 and 4. In zones 3 and 4 there was also a produced by regional metamorphism of mainly sedimentary rocks, glaucophane-schist metamorphism contemporaneous with this phase. the age of deposition and provenance of which are unknown. The Granodiorite intrusions into zone 2 occurred at this time as well as true age of the pre-U. Triassic metamorphism is not known. Kundig volcanic activity during the Eocene. The direction of folding and (1956) and Roever (1956) referred to the crystalline basement rocks thrusting, as well as the development of ophiolites in a belt around the as Palaeozoic or pre-Palaeozoic, but apparently without evidence Sula Spur, seem to indicate the important role that feature was playing other than regional considerations. In the South Arm of Sulawesi the in the evolution of this region. In addition the downwarping of zone 4 crystalline schists can only be shown to be pre-Cretaceous in age, but and perhaps parts of zones 2 and 3 in a belt around the Sula Spur their metamorphism is likely to have been of the same age as elsewhere. suggests a direct comparison with the U. Cretaceous downwarping Possible Permian history: The apparent absence of Permian rocks from of the Outer Banda Arc in front of the Australian shelf. Orogenic Sulawesi is surprising in view of the extensive Permian marine deposits movements were widespread in the Banda Arcs at this time. SULAWESI 373

I I

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I including some intrusives I Q TUKANG PLUTONIC ROCKS t 0~ BESI IS. ~ Granite & granodiorite i" SALAJAR IS. ~ ~'~ Basic rocks, including ophiolites V 'i" " Figure 6. Geological sketch map of Sulawesi (redrawn from a geological map published by the U.S.G.S. 1965). Blank areas in Sulawesi and the Sula Islands are areas for which no geological maps are known. 374 SULAWESI

Syn-orogenic (M. Eocene-L. Miocene) history: Eocene to Oligocene neritic 135 METAMORPHISMIN THE SULAWESI OROGENIG BELT deposits, mainly shelf limestone in zones 3 and 4, are thin and often Metamorphic rocks occur in all the four arms of Sulawesi, in some absent. This may be due to a period of uplift and erosion following the small nearby islands such as Kabaena and Butung and in several parts folding and introduction of ophiolites. In zone 2 a paralic facies de- of Central Sulawesi. The considerable literature on these rocks has veloped during Eocene to Oligocene times as well as some lime- been summarized by Rutten (1927), Brouwer (1947) and Bemmelen stones. The Eocene volcanic activity continued through Oligocene (1949) and the most recent publications are by Egeler (1947, 1948) and into Miocene times. and Roever (1947, 1950, 1953 and 1956). The general conclusions During the Oligocene the main orogenic phase of folding and reached by Roever (1953, 1956) are as follows: (1) The oldest phase thrusting occurred in the north of the South Arm (zone 2). There of regional metamorphism in Sulawesi occurred before the U. Triassic may also have been some fold movements in zone 3 and part of zone 4. and probably produced the epidote-amphibolite facies of Central Granodiorites and diorites were intruded into zone 2 during Eocene Sulawesi (zone 3) and the amphibolite facies of the South-east Arm, to Oligocene times. During the L. Miocene shelf limestones were Butung and Kabaena (zone 4). This regional metamorphic phase, widely deposited in Sulawesi, in zones 2, 3 and 4. which may even be pre-Palaeozoic according to Kundig (1956), Syn-orogenic (M. Miocene) history: The main orogenic phase in part belongs to an orogeny older than the Mesozoic-Cenozoic orogeny. of zone 4 (East Arm), involving folding and thrusting, occurred at this (2) A younger regional metamorphic phase which produced green- time. There is a suggestion of some fold movements at this time in schists and glaucophane schist facies in zones 3 and 4 is probably of zone 3 and the north of zone 2. The direction of thrusting was towards late Cretaceous or early Eocene age. (3) A phase of strong over- the Sula Spur. The M. Miocene was the time of a major orogenic thrusting in Kabaena (zone 4), which was post-Eocene in age (or phase in the Banda Arcs. possibly late Eocene or even mid-Eocene, as Kundig (1956) suggested @n-orogenic (U.Miocene-Pliocene) history: A molasse facies was de- for the East Arm) produced dynamic metamorphism. This dynamic veloped in zones 2, 3 and 4 during this interval, perhaps as a re- metamorphic phase may have also occurred contemporaneously in the sponse to uplift and erosion following the M. Miocene folding phase. North Arm (zone 2) (Brouwer 1934) and in the South-east Arm Very similar behaviour at this time is found in the Banda Arcs. et al. (zone 4). According to Kundig (1956) the greenschists and amphi- Locally neritic and littoral depgsits developed in zones 2, 3 and 4 and bolites in the East Arm (zone 4) were associated with the eruption of in zone 2 volcanoes were again active and important intrusions of the ophiolites. granodiorites occurred. Syn-orogenic (late Pliocene) history: Towards the end of the Pliocene there was a widespread period of folding in all parts of Sulawesi (zones 2, 3 and 4). Thrusts developed in the Butung Archipelago and B. SUBDIVISION OF THE SEGMENT the movements appear to be towards the west. This seems to be an anomalous feature of the regional tectonics and may indicate the The Sulawesi orogenic belt is here divided into five structural zones waning importance of the southern part of the Sula Spur, perhaps delimited somewhat arbitrarily at the 1000 m isobaths. The Banggai associated with its subsidence in that region, where the sea is now Islands have been included in the Sula Spur, which is regarded as a more than 4000 m deep. The U. Miocene to Pliocene granodiorite separate structural feature. intrusions of zone 2 may be associated with this orogenic phase. Zone 1 is wholly submarine, but has distinct northern and southern In zone 2 there was volcanic activity at this time. The late Pliocene parts, the Celebes Sea Basin (Krause 1966) and the Makassar Strait interval also saw a period of folding throughout most of the Banda Arc. Fracture. At the south of the Makassar Strait the sea floor shallows Post-orogenic (Quaternary) history: The Quaternary history of zones 2 and opposite Makassar the zone may be cut off" or pinch out. If and 4 appears to have been one of uplift and erosion, following the late zone 1 of the Sulawesi orogenic belt connects with zone 1 of the Banda Pliocene fold movements. The behaviour of zone 3 appears anomalous. Arc orogenic belt, then it must do so at 500 m between the Doang- The part of zone 3 in Central Sulawesi seems to have been uplifted and doang shoals and the coast near Makassar. There is some geophysical eroded, as were the Tongian Islands, whilst most of the zone is sub- evidence for regarding this broad ridge between the South Arm-- marine and may have subsided. Zone 1 subsided during the Quater- Paternoster Islands and east Java as a structural feature connecting the nary (Krause (1966). Zone 5 by analogy with zone 1 also possibly Western Celebes Arc with the Inner Sunda Arc of Java. The geo- subsided. It seems likely that in general the Quaternary evolution of logical history and igneous activity of these two regions offer support the region has emphasized the relief between the marine and non- for this idea. marine zones by adjacent processes of uplift and subsidence. Volcanic Zone 5 (the Foredeep) will be considered next, for like zone 1 it is activity has occurred during the Quaternary in the nolthern part of wholly marine. Where zone 5 lies on the convex, outer side of the zone 2 and in zone 3 (Una Una). Banda Arc orogenic belt it is a deep water zone always over 1000 m SULAWESI 375

Table 1 ZONES AND ELEMENTS IN SULAWESI

Zones

1 2 3 4 5 W. Celebes Celebes Arc and Western Part Sea N. Celebes Intra-Celebes E. Celebes of Age andfades of the Elements Basin Arc Arcs Zone Arc Foredeep Sula Spur

Quaternary Volcanics X X Quaternary Littoral and neritic X X X x not Obi Quaternary Evidence of subsidence x only Obi LATE-PLIOCENE OROGENIC PHASE M M M+S Pliocene Littoral and neritic x x x Miocene-Pliocene Granodiorite intrusive, x U. Miocene-Pliocene Molasse × × x U. Miocene-Pliocene Paralic U. Miocene-Pliocene Littoral and neritic x U. Miocene-Pliocene Volcanics x MID-MIOCENE OROGENm PHASE W W S+W Oligo-L. Miocene Volcanics x Oligo-L. Miocene Neritic x x x Eocene-Oligocene Granite, granodiorite and x diorite intrusives Eocene-Oligocene Neritic x x Eocene-Oligocene Paralic Eocene Volcanics U. Mesozoic-Eocene Glaucophane schists X X U. Mesozoic-Eocene Greenschists X X U. CRETACEOus-L. EOCENE OROGENIC PHASE S S+W W U. Cretaceous-L. Eocene Ophiolites x x only in Obi U. Cretaceous-L. Eocene Granodiorite intrusives U. Mesozoic Bathyal x x not Obi U. Mesozoic Neritic x ? in Obi L. Mesozoic Neritic and paralic x Juras, but no Trias UNCONFORMITY BELOW THE MESOZOIC SUCCESSION x x x Pre-U. Triassic Basement crystalline schists x x x

Note: x =present Principal orogenicphases: S=strong; M=moderate; W=weak. and locally over 4000 m deep. In the Sulawesi region zone 5 lies on 1969) and geologically poorly documented, so several alternative the concave side of the inner arc, and its disappearance from most of tectonic interpretations are possible. Although few epicentres of the Sulawesi orogenic belt may be associated with this reversal of intermediate and deep focus seismic earthquakes are reported from geometry. The interpretation of the relative positions of zone 5 and this part of zone 5 (of. Fitch 1970), we may not expect geophysical the Sula Spur in the Northern Banda Sea is open to discussion, analogy with zone 5 of the Banda Arcs, because the nearby deep however. The identification of the deeper water ( > 1000 m) immedi- Philippine trench and the volcanoes of Halmahera have no equivalents ately west of the Halmahera Islands as the continuation of zone 5 of on the convex side of the zone 5 of the Banda Arcs. the Sulawesi orogenic belt is one that might not find general acceptance, Zone 2. The western limits of zone 2 are drawn arbitrarily at the but it does seem to occupy the outside of the convex outer arc (of the 1000 m isobath, except south of Makassar where (as discussed for North Moluccan Arc). This region between Sulawesi and Irian Barat zone 1 above) the limit is taken at the 500 m isobath until near the is geophysically complicated (el. Fitch 1970; Hatherton & Dickinson trench in the Flores Sea. From there the margins of zone 2 continue 376 SULAWESI eastward as part of the Salajar-Lucipara Arc at much greater depths map and with some support from shallow focus seismic activity in the Banda Sea. The inner margin of zone 2 is drawn at the 1000 m (Fitch 1970), appears to be a more consistent interpretation than that isobath until the Banda Sea. This eastern margin coincides locally offered by Klompe (1954). with the submarine fault scarp on the east of the South Arm which One problem is the relationship of the possible western extension of extends from the Tawaelia graben in Central Sulawesi to the east of the Sorong Fault zone, to the north edge of the Sula Spur. Visser & Salajar. In the north the margin separates the Sangihe ridge and Hermes (1962) suggested the fault extended south of Obi and south islands from the Gorontalo Trough and the Sangihe Trough. The of the Sula Islands. Alternatively it may extend south of Obi but northern part of zone 2 (Northern Celebes Arc) is characterized by north of the Sula Islands, so that west of Obi it could coincide with the a line of active volcanoes and a zone of epicentres of intermediate north limit of the Sula Spur, or it could occur north of Obi separating focus earthquakes. that island from the Halmahera Islands; this last interpretation might Zone 3 may be called the Intra-Celebes Arcs zone. Mostly it is account for a line of shallow focus seismicity along the postulated submarine and is deeper than 1000 m or even than 9000 m. Two land extension (Fitch 1970). The south margin of the west part of the Spur areas are involved in this zone, one is the Poso zone of Central Sulawesi presents the greatest problem; the positive isostatic gravity anomaly and the other is the Tongian Islands and the volcano of Una Una. extends south into the north of the Banda Sea where the sea floor On Sulawesi the western margin of the zone is coincident with the drops rapidly to 4000 m south of the Sula Islands. The present writer Tawaelia graben and its northern and southern submarine exten- follows Klompe (1954) in drawing this south margin around the sions. In the south this zone is continuous with the Intra-Banda Arcs southern limit of the gravity anomaly; this seems to accord most trough (zone 3 of the Banda Arcs). Zone 3 is coincident with a zone closely with the tectonic behaviour of the East Celebes Arc and the of positive isostatic gravity anomalies over most of its length in the Outer and Inner Banda Arcs, although this hypothesis receives no Sulawesi belt, but this feature does not continue into zone 3 of the support from present seismic activity. Banda orogenic belt. Zone 4 is the East Celebes Arc, which to the south and north continues with structures called the Tukang Besi Arc and the North C. STRUCTURAL RELATIONSHIPS Moluccan Arc respectively. At the southern end the arc is inter- OF THE SULAWESI ARCS WITH preted to be continuous along strike with the Outer Banda Arc NEIGHBOURING REGIONS (zone 4 of the Banda Arcs orogenic belt. The zone is characterized in both the Sulawesi and Banda orogenic belts by a strong zone of Sulawesi separates four major geological provinces: to the west and negative isostatic gravity anomalies. The seismic isobaths drawn by south-west are the Larger Sunda Islands and their shelf, partly Hatherton & Dickinson (1969) suggest important differences between represented by Borneo and Java; to the south and south-east are the zone 4 of the Banda Arcs and part of zone 4 of Sulawesi (the South- Lesser Sunda Islands which form the Banda Arcs; to the east is the east Arm). Their contours suggest, however, that the East Arm of Vogelkop and Bomberai of Irian Barat (formerly called west New Sulawesi may occupy a similar position to an inclined seismic zone as Guinea); to the north are the Philippines which form part of the that indicated for the Outer Banda Arc. island chains that mark the boundary of the western Pacific. Each The Sula Spur: Stille (1945) and Klompe (1954) regarded the Sula different part of Sulawesi appears to have geological affinity with some Spur as a detached part of the Australian continent. Kundig (1956) important aspects of one or more of these four major geological referred to it as a 'small stable intra-orogenic craton'. Wegener (1966) provinces. On the basis of the linear belt of strongly negative gravity interpreted it as a structure due to New Guinea penetrating the region anomalies that characterize the East and South-East Arms of Sulawesi, of the Banda Arcs by the north-west drift of Australia relative to Asia. the East Celebes Arc has been regarded (Kuenen et al. 1934) as an Fitch (1970) claimed that seismic evidence suggests the Sula Spur extension of the Outer Banda Arc (structural zone 4). It is believed to 'currently includes one or more plates of lithosphere'. continue northwards into the North ~vIoluccan Arc (Visser & Hermes The north margin of the western part of the Sula Spur is drawn 1962). There is uncertainty about the correlation on gravity data at the 1000 m isobath. Klompe (1954), and others later, took this between Butung at the south of the South-East Arm and Buru because margin through the middle of Obi so as to exclude the ophiolites. The this part of the Banda Sea does not display the strong negative gravity present writer follows Kundig (1956) and Fitch (1970) and considers values that characterize zone 4 elsewhere. Westerveld (1955) noted on the basis of the geological history, the isostatic gravity map and the that the submarine floor of this part of zone 4 was marked by a series shallow focus seismic activity that the northern limit of the Sula Spur of strong ridges and trenches striking NW-SE, which he suggested should be drawn north of Obi. Eastward from Obi the northern limit probably marked the sites of transverse faults striking in that direction. is here drawn at the north edge of the Obi-Pisau-Kafiau-Batanta The absence of the strong negative gravity values may be associated ridge, which on the basis of topography, the isostatic gravity anomaly with such faults. The correlation of the Outer Banda Arc with the SULAWESI 377

East Celebes Arc has also been proposed on the basis of these lands of what he called the 'foreland belt' that included Sula, Obi and western possessing a Mesozoic (and possibly Palaeozoic) history that dis- Bomberai. Visser & Hermes (1962) and Hermes (1968) considered tinguishes them from all the surrounding regions. Umbgrove (1938) that Misool and western Bomberai form part of the Banda Arc prin- and Teichert (1939) referred to this zone 4 as the Timor--East cipally because they were submerged during most of Mesozoic time. Celebes Geosyncline, and Teichert thought it an extension of the The present author favours the interpretation that regards Misool and Westralian Geosyncline of the Carnarvon basin. western Bomberai as part of the Sula Spur and distinct from the Banda The South Arm of Sulawesi, together with the Palu zone of the Arcs. central region and the North Arm, expose granite intrusions and Although the definition of the limits and correlation between the acid extrusives which suggests some affinity between this zone 2 and various structural zones of Sulawesi and the neighbouring island arcs the larger Sunda Islands (Borneo, Java & Sumatra). In contrast, in is open to debate, it is generally acknowledged (Umbgrove 1949; the East and South-East Arms extensive outcrops of ultrabasic and Holmes 1965) that Sulawesi represents the junction of two major basic igneous rocks predominate, which as Brouwer (1930) observed Tertiary orogenic belts, one is the Himalayan-Indoburman-Indonesian are characteristic of the Banda Arcs. orogenic belt and the other a branch of the Circum-Pacific orogenic The North Arm of Sulawesi is usually regarded as a southerly belt. extension of the chains of island arcs around the western Pacific. The Philippine Arc passes south of Mindanao into a submarine ridge with islands and then into the Minahasa portion of the North Arm. This correlation is based on the strong topographical feature with D. REFERENCES accompanying chain of active volcanoes (zone 2) which separates the belt of strong negative gravity anomalies of the North Moluccan Arc BEMMELEN, R. W. VAN. 1949. The Geology of Indonesia. The Hague (Government Printing Office). (zone 4) from the strong positive anomalies of the Celebes Sea (zone 1). BLOW, W. H. 1969. Late Middle Eocene to Recent planktonic foraminiferal bio- The structural relationship of the South Arm and the western part of stratigraphy. In: Bronniman, P. & Renz, H. H. (Eds.), Proceedings 1st Inter- Central Sulawesi (zone 2) to zones 3 and 4 is uncertain. The south of national Conference on Planktonic Microfossils, Geneva (1967), vol. 1. Leiden (Brill), zone 2 lacks active volcanoes (Neumann van Padang 1951) and strong pp. 199-421. BOTHE, A. CH. D. 1927. Voorloopige mededeeling betreffende de geologic van gravity anomalies in Sulawesi. The acid igneous rocks of this region Zuidoost Celebes. De Mijningenieur, 8, 97-103. have suggested some possible affinity with the Larger Sunda Islands BROUWER, H. A. 1919. Geologisch overzicht van her oostelijk gedeelte van den Oost- to the west and south, but Westerveld (1955) proposed that this Indischen Archipel. 07aarb. M~inw. Ned.- Oost-Indig, 1917, 2, 145-452. region was an extension of the Inner Banda Arc. He suggested that the -- 1921. Geologische onderzoekingen op de Soela Eilanden. 07aarb. MOnw. Wed.- southern part of the South Arm was part of an arc that connected Oost-Indi~, 1920, 2. 1924. Bijdrage tot de geologic der Obi-eilanden. 07aarb. Mijnw. Wed.-Oost- Salajar with the Banda Islands through a series of submarine ridges Indig, 1923, 63-136. with a few islands such as Komba, Gunungapi and the Lucipara 1930. The major tectonic features of Celebes. Proc. K. ned. Akad. Wet. 33, Islands. This arc is characterized by weak positive isostatic anomalies 338-43. and locally in the Banda and Flores Seas by active volcanoes. At the --1941. Tektonik und Magma in der Insel Celebes und der indonesische Gebirgstypus. Proc. K. ned. Akad. Wet. 44, 253-61. present time there seems to be insufficient available geological or --1947. Geological explorations in Celebes: Summary of the results. In'. Geo- geophysical evidence to support or reject this hypothesis. logical Explorations in the island of Celebes. Amsterdam (North-Holland), pp. 1-64. Two major strike slip faults, called the Sorong Fault zone and the BROUW~R, H. A., H~TZEL, W. H. & STRAET~R, H. E. G. 1934. Geologische onderzoe- Tarera-Aidoena Fault zone in Irian Barat by Visser & Hermes (1962), kingen op het eiland Celebes. Verh. K. ned. geol.-m~jnb. Genoot. 10, 39-171. may through their possible westward extension have influenced the BRUYN, J. W. de. 1951. Isogam maps of Caribbean Sea and surroundings and of southeast Asia. WldPetrol. Congr. 3, 1,598-612. development of the major arcuate zone of the East Celebes Arc and DIECKMANN, W. • JULIUS, M. W. 1925. Algemeine geologie en ertsofzettingen van its extensions into the Philippine and Banda Arcs. Zuidoost Celebes. 07aarb. Mijnw. Wed.-Oost-Indig, 1924, 11-65. Stille (1945) and Klompe (1954) suggested that the region of the EGELER, C. G. 1947. Contribution to the petrology of the metamorphic rocks of Sula and Banggai Islands where crystalline schists crop out, may repre- western Celebes. In: Geological explorations in the island of Celebes. Amsterdam (North-Holland), pp. 177-346. sent a detached fragment of the Australian continent. The western part -- 1948. On amphibolitic and related rocks from Western Celebes and the of this Sula Spur is characterized by a strong positive gravity anomaly. southern Sierra Nevada. California. Proc. If. ned. Akad. Wet. 51, 100-5 In Figs. 1, 2 and 4 the eastward extension of this Spur is shown to FITCH, T.J. 1970. Earthquake mechanisms and island arc tectonics in the Indonesian- include the island of Obi and a south-eastward extension is suggested Philippine region. Bull. Seismol. Soc. Am. 60, 565-91. to include Misool and part of south-western Bomberai. Stille (1945) FITCH, T.J. & MOLNAR,P. 1970. Focal mechanisms along inclined earthquake zones in the Indoneslan-Philippine region. 07. geophys. Res. 75, 1431-44. regarded Misool as part of the Sula Spur and Bemmelen (1949, p. 458) GUTENBERG, B. & RICHTER, C. F. 1954. Seismicity of the Earth and related phenomena. considered that Misool does not belong to the Banda Arcs but is part 2nd edn. New Jersey (Princeton University Press). 378 SULAWESI

HATHERTON, T. & DICKINSON, W. 1~.. 1969. The relationship between andesitic ROEVER, W. P. DE. 1947. Igneous and metamorphic rocks in eastern central Celebes. volcanism and seismicity in Indonesia, the Lesser Antilles, and other island arcs. In: Geological explorations of the island of Celebes. Amsterdam (North-Holland), 07. geophys. Res. 74, 5301-10. pp. 67-173. HERMES, J. J. 1968. The Papuan geosyncline and the concept of geosynclines. Geol. 1950. Preliminary notes on glaucophane-bearing and other crystalline schists Mijnb. 47, 81-97. from south-east Celebes, and on the origin of glaucophane-bearing rocks. Proc. HeTZEL, W. H. 1935. Enkele kritische aanteckeningen bij een recente publicatie over If. ned. Akad. Wet. 53, 1455-65. de Geologic van den Oostarm van Celebes. De Ingenieur in Ned. Ind. 2 (4), IV, 1953. Tectonic conclusions from the distribution of metamorphic facies in the 29-31. island of Kabaena, near Celebes. Proc. Pacific Sci. Congr. (New Zealand, 1949), 1936. Verslag van het onderzoek naar het voorkomen van asfaltgesteenten 7, 2, 71-81. op het eiland Boeton. Wet. Meded. Dienst. Mijnb. Ned.-Oost-Indig, 21. --1956. Some additional data on the crystalline schists of the Rumbia and HOLMES, A. 1965. Principles of physical geology. 2nd edn. London (Nelson). Mendoke mountains, south-east Celebes. Verh. K. ned. geol.-mijnb. Genoot. 16, KATIL~, J. A. 1970. Large transcurrent faults in southeast Asia with special reference 385-93. to Indonesia. Geol. Rdsch. 59, 581-600. RoY, B. C. (co-ordinator). 1961. Geological map of Asia and Far East (1:5,000,000) KLOMPE, TH. H. F. 1954. The structural importance of the Sula Spur (Indonesia). (ECAFE.) Indones..y. nat. Sci. 110, 21-40. RUTTEN, L. M. K. 1927. Voordrachten over de geologic van Nederlandsch Oost-Indig. 1957. Pacific and Variscan orogeny in Indonesia. Indones. ~7. nat. Sci. 113, Groningen-Den Haag (Wolters U.M.). 43-87. STXLLE, H. 1945. Die tektonische Entwicklung des hinterindischen Festlands und KOOLHOVEN, W. C. B. 1930. Verslag over eene verkenningstocht in den Oostarm van Inselgebiete. Geotekt. Forsch. 7, 1-34. Celebes en den Banggai-archipel. aTaarb. Mijnw. Wed.-Oost-Indig, 1929, 187-228. TECTONIC MAP OF EURASIA (SCALE 1:5,000~000). 1966. Moscow (Akad. nauk SSSK). 1932. De Geologic van her Maliliterrein (Midden Celebes). j?aarb. Mijnw. TEICHERT, C. 1939. The Mesozoic transgressions in Western Australia. Austr. 3. Sci. Wed.-Oost-Indig, 1930, 3, 127-53. 2, 84--6. KOPERnERG, M. 1929 & 1930. Bouwstoffen voor de geologic van de Residentie UMBGROV~, J. H. F. 1935. De Pretertiaire historic van den Indischen Archipel. Leid. Menado. oTaarb. Mijnw. Ned.-Oost-Indig, 1928, 1 and 2. geol. Meded. 7, 119-55. KRAUSE, D. C. 1966. Tectonics, marine geology and bathymetry of the Celebes Sea- -- 1938. Geological history of the East Indies. Bull. Am. Ass. Petrol. Geol. 22, Sula Sea region. Bull. geol. Soc. Am. 77, 813-32. 1-70. KtmN~N, PH. H., UMBGROVe, J. H. F. & VENING MEINESZ, F. A. 1934. Gravity, 1949. The structural history of the East Indies (Cambridge University Press). geology and morphology of the East Indian Archipelago. In: Gravity expeditions UNITED STATES GEOLOGIC SURREY. 1965. Geologic map of Indonesia--Eastern half. at sea, 1923-1932. Vol. II, The interpretation of the results. Netherlands Geodetic 1:2,000,000. Misc. geol. Inv. Map. 1--414. Commission, pp. 107-94. VXSSER, W. A. & HERMES, J. J. 1962. Geological results of the exploration for oil in KUNDm, E. 1932. Versuch einer petrographischen Characteristik des Kristallinen Netherlands New Guinea. Verb. If. ned. geol.-m~]nb. Genoot. 20, 1-265. Grundgebirges von Celebes. Schweiz. miner, petrogr. Mitt. 12, 450-507. VLERK, I. M. VAN DER & DOZY, J. J. 1934. The Tertiary rocks of the Celebes expedi- 1956. Geology and ophiolite problems of east-Celebes. Verb. If. ned. geol.- tion, 1929. Verh. If. ned. geol.-rn~]nb. Genoot. 10, 183-217. m~inb. Genoot. 16, 210-35. VLERK, I. M. VAN DER & UMBGROVE,J. H. F. 1927. Tertiaire gidsforaminiferen van KtrrAss,,', A. YON. 1934. Her Paleozoicum en de Trias van Oost Celebes. Verb. If. ned. Nederlandsch Oost-Indie. Wet. Meded. Dienst. Mijnb. Wed.-Oost-Indi8, 6. geol.-m~inb. Genoot. 10, 295-305. WEGENER, A. 1966. The origin of continents and oceans. 4th edn. London (Methuen). Ia~ PICHON, X. 1968. Sea-floor spreading and continental drift. J. geophys. Res. 73, WP..STERVELD, D.J. 1955. The Lucipara Islands ridge and a third arc in the Banda 3661-705. Sea. Geol. Mijnb. 17, 84-8. LoezY, L. YON. 1933--4. Geologic van Noord Boengkoe en het Bongka gebied tusschen WILLIAMS, H. W. V. 1937. Contribution to the petrology of the crystalline schists of de Golf van Tomini en de Golf van Tolo in Oost Celebes. Verb. If. ned. geol.- western central Celebes. Doctoral thesis, University of Amsterdam. mijnw. Genoot. 10, 219-27. WITKAMP, H. 1940. Langs het stroomgebied van de Lariangrivier (West Celebes). NAGASAKA, K. 1971. Terrestrial heat flow in the Celebes Sea and the Sula Sea. Tijdschr. If. ned. aardrijksk Genoot. 47, 581-600. Marine geophys. Res. WUNDERLIN, W. 1913. Beitr~ige zur Kenntnis der Gesteine yon Sfidost-Celebes. NEUM~'~N W~'~ PADANG, M. 1951. Catalogue of the active volcanoes of the world including Samml. geol. Reichsmus. Leiden, Ser. 1, 9, 244-80. solfatarafields. Part 1, Indonesia. (Int. Ass. Vulc.) RITSEMA, H. R. & VELDK~'~P, J. 1968. Fault plane mechanisms of southeast Asian earthquakes. Meded. Verh. If. ned. met. Inst. 76, 63.