ELSEVIER Palaeogeography, Palaeoclimatology, Palaeoecology 145 (1999) 303±337

Cenozoic palaeogeographic evolution of Sulawesi and Borneo

Moyra E.J. Wilson Ł, Steve J. Moss 1 SE Asia Research Group, Department of Geology, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK Received 30 September 1997; revised version received 1 July 1998; accepted 6 July 1998

Abstract

Sulawesi and Borneo are located in the middle of the Indonesian Archipelago, an area which has been extremely tectonically active throughout the Cenozoic. This paper compiles current knowledge on the geology and palaeogeography of this complex region and includes the ®rst attempt to synthesise palaeogeographic data onto plate tectonic reconstructions. Construction of palaeogeographic maps helped to identify some of the strengths and weaknesses of current plate tectonic models for the region, thereby highlighting areas where further geological research is required. Palaeogeographic maps presented, using plate tectonic reconstructions as a base, illustrate the evolution of Borneo and Sulawesi and highlight important changes in the environment during the Cenozoic. The Tertiary geological history of eastern Borneo and Sulawesi is inextricably linked to the progressive accretion of continental and oceanic material from the east, onto the eastern margin of Sundaland, and to the resultant development of volcanic arcs. Large tracts of western Sulawesi, eastern Borneo, the East Java Sea and the Makassar Straits formed an extensive basinal area throughout much of the Tertiary. Implications for plate tectonics, exploration for natural resources and biogeography are discussed from the palaeogeographic reconstructions of Sulawesi and Borneo.  1999 Elsevier Science B.V. All rights reserved.

Keywords: palaeoenvironments; palaeogeography; tectonics; Cenozoic; Southeast Asia; biogeography; resources

1. Introduction neo are frontier exploration provinces for many nat- ural resources, such as hydrocarbons, minerals, coal, The islands of Borneo and Sulawesi lie in the material for use in the construction, agricultural or midst of an extremely complex tectonic region where pharmaceutical industries. A knowledge of the re- three major plates; the Indo-Australian, Philippine- gional variations in palaeogeography through time, Paci®c and Asian plates interact and collide (Fig. 1). when combined with information such as strati- The areas between these major plates is a compos- graphic thicknesses or nature of volcanism may ite domain of smaller microcontinental and oceanic provide a useful tool for the exploration of these fragments and a region where volcanism has been natural resources. An understanding of the evolution common throughout the Tertiary. Sulawesi and Bor- of this region is also of critical importance to bio- geographers, since Wallace's original faunal divide runs between the two islands, and is now taken to Ł Corresponding author. Tel.: C44-17844-43592; Fax: C44- 17844-34716; E-mail: [email protected] represent the eastern boundary of Asiatic biota. 1 Present address: Robertsons Research Australia Pty Ltd., 69 A range of geological information suggests that Outram Street, West Perth, W.A. 6005, Australia. large areas of Kalimantan and western Sulawesi had

0031-0182/99/$ ± see front matter c 1999 Elsevier Science B.V. All rights reserved. PII: S0031-0182(98)00127-8 304 M.E.J. Wilson, S.J. Moss / Palaeogeography, Palaeoclimatology, Palaeoecology 145 (1999) 303±337 d Borneo. Modi®ed after Hamilton (1979), Hutchison (1989), Daly et al. (1991), Parkinson (1991), Van de Weerd and Armin (1992) and Hall (1996). Fig. 1. Regional tectonic setting of Sulawesi and Borneo and the distribution of pre-Mesozoic cratonic areas and Tertiary basinal area in Sulawesi an M.E.J. Wilson, S.J. Moss / Palaeogeography, Palaeoclimatology, Palaeoecology 145 (1999) 303±337 305 been juxtaposed and attached to southwestern Bor- thought to delineate regions of Asiatic and Aus- neo, part of the eastern margin of Sundaland, ªthe tralian ¯ora and fauna, runs through the Makassar stable core of SE Asiaº, by the Late Cretaceous Straits between the two islands and also between (Metcalfe, 1996). Tertiary subduction of the Indian Bali and Lombok. This original faunal divide is Ocean, Philippine Sea and Molucca Sea plates was now taken as the western boundary of Wallacea responsible for the progressive collision, accretion (Dickerson, 1928), which is best described as a bio- and assimilation of fragments of continental and geographic region with a high degree of endemism oceanic crust along the eastern margin of Sunda- situated between areas with Asiatic and Australian land. Around the eastern and southern margins of ¯oras and faunas (George, 1981; Whitten et al., Sundaland, within this overall compressional, sub- 1987). The Makassar Straits appears to have been a duction-related regime, various extensional episodes barrier to dispersal for many groups of animals, al- have resulted in the formation of extensive sedi- though the clear faunal contrast (Earl of Cranbrook, mentary basins and in some cases, marginal oceanic 1981; Briggs, 1987; Musser, 1987) is not re¯ected to basins developed (the South China, Sulu and Celebes the same extent by the ¯ora (George, 1981; Van Bal- seas; Fig. 1). gooy, 1987). Regional plate tectonic changes have During the last twenty years several Tertiary plate been related to biogeography by a number of au- tectonic reconstructions have been developed for thors (Audley-Charles et al., 1981; Audley-Charles, Southeast Asia (Carey, 1975; Hamilton, 1979; Ran- 1981, 1987; Burrett et al., 1991; Hall, 1998). This gin et al., 1990; Daly et al., 1991; Lee and Lawver, work concentrates on Borneo and Sulawesi and sum- 1994, 1995; Hall, 1996). There is now a growing marizes how the Cenozoic plate tectonic variations consensus over some of the main points of the plate and the changes in palaeoenvironment may have tectonic evolution of the area, although detailed el- affected past migrations=dispersals. A detailed dis- ements of the reconstructions and the mechanisms cussion of this topic can be found in Moss and driving plate tectonics are still under dispute. Com- Wilson (1998). paring local palaeogeographic information with re- The future potential economic growth of South- gional reconstructions is one way to test the validity east Asia is in part dependent on utilising its wealth of these reconstructions by highlighting matches or of natural resources. Borneo and Sulawesi are both discrepancies in the inferred tectonic setting and dis- areas of proven coal, hydrocarbon, minerals and tribution of depositional environments. However, un- building material accumulations and considerable til now for Borneo and Sulawesi, palaeogeographic effort is being put into exploration for further dis- reconstructions have only been drawn on a local coveries. The location and amounts of these natural scale and rarely within a plate tectonic context. Al- resources depends on the geological evolution of the though we are limited by the incomplete nature of area and the past distribution of environments, re- the geological record or by imperfections in our sulting in the formation of certain rock types and the knowledge of the geology, for areas where data are economic accumulation of natural resources. There- good a reliable test can be made. The ®rst and often fore constructing palaeogeographic maps is a useful most critical step in plate tectonic reconstructions is tool for furthering the exploration of natural re- to delimit which areas formed plate boundaries and sources, and particularly in the hydrocarbon industry to evaluate how the nature of these plate margins this method is routinely used. varied through time. A study of facies variations can help to evaluate discontinuities or possible connec- tions between regions. Comparing palaeogeographic 2. Data sources, quality and methodology data with plate tectonic reconstructions also high- lights gaps in the geological data base and suggests The bases for the plate tectonic template used key areas for future research. in this paper are the recent reconstructions of Hall Borneo and Sulawesi are of prime importance to (1996) which incorporate new data from eastern In- biogeography and palaeobiogeography of Southeast donesia to help constrain the motion of the Philippine Asia. The faunal divide of Wallace (1863), originally Sea Plate (Hall et al., 1995). Many reconstructions of 306 M.E.J. Wilson, S.J. Moss / Palaeogeography, Palaeoclimatology, Palaeoecology 145 (1999) 303±337 the region imply major strike-slip faulting following et al., 1990; Fuller et al., 1991, 1999; Sunyata and India's collision with the Eurasian margin (Peltzer Wahyono, 1991; Moss et al., 1997) for southern and Tapponnier, 1988; Rangin et al., 1990; Daly et Borneo and the South Arm of Sulawesi for the Ter- al., 1991; Lee and Lawver, 1994, 1995). The Indian tiary. Since different timing and amounts of rotation collision is seen in all these reconstructions as the would have affected the evolution and accretion of major driving force controlling Tertiary tectonics of material forming eastern Sulawesi and the nature Southeast Asia. The reconstruction of Hall (1996) of the change between northern mainland Borneo still recognizes the important in¯uence of major and the South China Sea, the 45ë counterclockwise strike-slip faulting in Southeast Asia (with displace- rotation of Hall (1996) remains in the palaeogeo- ments of about 500 km, after Briais et al., 1993). graphic reconstructions shown. However, there is a However, the major driving forces are suggested to need for further local and regional palaeomagnetic be the motions of the Philippine Sea Plate and col- work to better understand the rotational history of lision of the Australian plate (Hall, 1996). Although the islands. these reconstruction differ in terms of their detail The series of palaeogeographic maps presented and mechanisms, most of Borneo and Sulawesi do here illustrate the evolution of Borneo and Sulawesi not differ signi®cantly for the purposes of plotting during the Cenozoic. The data used in constructing palaeogeographic data. these palaeogeographies were derived from an exten- Compiling palaeogeographic data onto selected sive literature review and considerable ®eldwork by timeslices of the reconstruction highlighted regions London University SE Asia Research Group on Bor- which were incompatible from a palaeogeographic neo and Sulawesi. These maps have been constructed point of view, thereby providing a test for the plate using all the available geological evidence, including tectonic reconstructions. The Atlas program used by facies, stratigraphic, biostratigrapic, igneous, meta- Hall (1996) to reconstruct the Tertiary history of the morphic, structural and palaeomagnetic data. Signif- region only allowed a certain number of tectonic icant gaps exist within the data set, and particularly fragments to be de®ned and internal deformation for some of the remoter areas there is limited in- could not be modeled within these fragments. In a formation. The maps represent time slices, and as region which was variously undergoing extension, such are attempts to show the environments which compression, transtension or transpression it is un- are inferred to have existed around that moment in likely that the individual blocks de®ned would have time. The time slices shown were chosen to best acted rigidly. Therefore, depending on the stress illustrate key periods in the palaeogeographic evolu- regime for different areas some internal deformation tion of these islands. In some areas, marked changes has been incorporated and in certain areas, partic- in environment may have taken place before, be- ularly in Sulawesi, the reconstructions used differ tween and after the time slices shown. Periods of slightly from those of Hall (1996) as suggested by non-deposition and erosion are not shown on the the palaeogeographic data. diagrams although they have been recognised in The rotation history of Borneo and western Su- the sedimentary record in several basins. Previous lawesi is still highly contentious. Hall's (1996) re- attempts at palaeogeographic reconstruction have ei- construction incorporated a counterclockwise rota- ther been limited to small areas, such as hydrocarbon tion of southern Borneo and western Sulawesi of 45ë exploration blocks (Wain and Berod, 1989) or very between 20 and 10 Ma. However, it is recognised generalised palaeogeographies for very long time pe- that regional and local block rotations are dif®cult to riods (Umbgrove, 1938; Beddoes, 1980; Rose and distinguish and interpret on the basis of the current Hartono, 1978; Van de Weerd and Armin, 1992; Su- palaeomagnetic data available for the region (Rangin darmono et al., 1997). As far as we know this is et al., 1990; Ludmadyo et al., 1993; Lee and Lawver, the ®rst attempt to synthesise palaeogeographic and 1994; Hall, 1996; Moss et al., 1997). Various authors plate tectonic data, creating meaningful palaeogeo- either favour no rotation (Ludmadyo et al., 1993; graphic reconstructions for the whole area of Borneo Lee and Lawver, 1994) or variable amounts of coun- and Sulawesi. terclockwise rotation (Haile et al., 1977; Schmidtke M.E.J. Wilson, S.J. Moss / Palaeogeography, Palaeoclimatology, Palaeoecology 145 (1999) 303±337 307

3. Geology and tectonics of Borneo and Sulawesi granites which intrude deformed basic and ultrabasic rocks, a melange zone and cherts of probable Juras- Sulawesi and Borneo are situated in a tectonically sic to Cretaceous age (Amiruddin, 1989; Heryanto et complex region between three major plates. The al., 1993; Harahap, 1995). Upper Cretaceous to lower present-day setting is mirrored by the complexity of Tertiary turbidites of the Rajang and Embaluh groups the pre-Tertiary and Tertiary geology of these two comprise much of the Central Kalimantan Ranges islands, which is brie¯y reviewed below. and have also been intruded by Cretaceous granites in places (Pieters and Supriatna, 1990; Fig. 2). An 3.1. Borneo accretionary prism origin has been inferred for the lithologies in the Central Kalimantan Ranges (Hamil- Borneo is bounded by three marginal basins (South ton, 1979), although Moss (1998) suggested a rem- China, Sulu and Celebes seas), microcontinental frag- nant oceanic basin depositional setting for the tur- ments of south China origin (Dangerous Grounds, biditic lithologies. Cretaceous shelf sandstones (Se- Reed Bank) to the north-northeast, mainland South- langkai Formation), limestones, Triassic granites and east Asia (Indochina and Peninsula Malaysia) to the older metamorphic rocks also occur in the centre of west-northwest and the Javanese volcanic arc to the Borneo (Pieters and Supriatna, 1990; Fig. 2). A wide south (Figs. 1 and 2). Borneo has been interpreted variety of tectonically intercalated sedimentary, meta- as the product of Mesozoic accretion of ophiolitic morphic and basic to ultrabasic igneous rocks occur in material, marginal basin ®ll, island arc material and the Meratus Mountains (Fig. 2). These have been in- microcontinental fragments onto the Palaeozoic con- terpreted as back-arc oceanic material and associated tinental core of the Schwaner Mountains in the south- volcanic and sedimentary rocks accreted and thrust west of the island (Fig. 2; Hutchison, 1989; Metcalfe, onto the eastern margin of the Sundaland craton in 1996). Borneo formed a promontory on the south- the Early Cretaceous (Sikumbang, 1986, 1990). The eastern margin of Sundaland, the stable margin of Mesozoic geology of Borneo is reviewed in greater the Eurasian plate by the Tertiary. East of Borneo, detail in Tate (1991) and Moss (1998). and separating it from Sulawesi are the deep North Major tracts of eastern, central and northern and South Makassar Basins (Fig. 2), comprising the Borneo are covered by Tertiary sedimentary rocks Makassar Straits, the formation of which was initiated (Fig. 2), which were deposited in lacustrine, ¯uvial by the middle Eocene (Situmorang, 1982). Two NW± marginal-marine or marine environments (Fig. 4). SE-trending fault zones bound the North Makassar The depocentres, were often laterally interconnected, Basin to the north and south, respectively. locally through intricate and narrow links (Fig. 2; Pre-Tertiary rocks occur in the southwestern Pieters et al., 1987; Pieters and Supriatna, 1990). (Schwaner Mountains) and eastern (Meratus Moun- Tertiary sediments rest unconformably on variably tains) parts of Borneo and from northeast to south- deformed pre-Tertiary units (Hutchison, 1996a) and west across the island (Central Kalimantan Ranges; earlier basement structures in¯uenced basin evolu- Fig. 2). The Schwaner Mountains include Palaeo- tion (Cloke et al., 1997). Tertiary sedimentation oc- zoic metamorphic rocks intruded by numerous Creta- curred contemporaneously with, and subsequent to, ceous granites and tonalites, and this area is thought a period of Palaeogene extension and subsidence, to have formed part of the stable Sundaland cra- which had begun by the middle Eocene (Hutchison, ton during the Mesozoic and Cenozoic. Permo-Tri- 1996a; Moss et al., 1997; Moss and Finch, 1998; assic schists, gneisses, granites, gabbros and serpen- Moss and Chambers, 1999). The Tertiary sedimen- tinites also crop out within the Busang and Embuoi tary history in Borneo was punctuated by several complexes, located at the eastern and western ends phases of volcanic activity (Fig. 4). of the Ketungau Basin, respectively, and are possi- bly bounded by low-angle detachment faults (Fig. 2; 3.2. Sulawesi Pieters and Supriatna, 1990). To the north of the Schwaner Mountains and within the Central Kaliman- Sulawesi is formed of distinct N±S-trending tec- tan Ranges are other smaller Cretaceous (131±75 Ma) tonic provinces (Fig. 3; Sukamto, 1975), which are 308 M.E.J. Wilson, S.J. Moss / Palaeogeography, Palaeoclimatology, Palaeoecology 145 (1999) 303±337

Fig. 2. Simpli®ed geological map of Borneo after references given in the text. M.E.J. Wilson, S.J. Moss / Palaeogeography, Palaeoclimatology, Palaeoecology 145 (1999) 303±337 309

Fig. 3. Simpli®ed geological map of Sulawesi after references given in the text. Tectono-stratigraphic subdivisions and names of different areas of Sulawesi used in the text are also shown. thought to have been sequentially accreted onto Sun- pretations of the available data, the evolution and daland during the Cretaceous and Tertiary. These juxtaposition of fragments within Sulawesi remains tectonic provinces, moving from west to east, are highly contentious. An attempt has been made to the Western Sulawesi Plutono-Volcanic Arc, the describe the alternative hypotheses and to evaluate Central Sulawesi Metamorphic Belt, the East Su- the implications of these varying interpretations. lawesi Ophiolite and the microcontinental blocks of The Western Sulawesi Plutono-Volcanic Arc, com- Banggai±Sula and Buton±Tukang Besi (Sukamto, prising the North and South Arms of Sulawesi, is 1975; Hamilton, 1979; Parkinson, 1991). In part composed of thick Tertiary sedimentary and volcanic due to a lack of information, and to different inter- sequences overlying pre-Tertiary tectonically interca- 310 M.E.J. Wilson, S.J. Moss / Palaeogeography, Palaeoclimatology, Palaeoecology 145 (1999) 303±337 M.E.J. Wilson, S.J. Moss / Palaeogeography, Palaeoclimatology, Palaeoecology 145 (1999) 303±337 311 lated metamorphic, ultrabasic and marine sedimen- quence (Bergman et al., 1996) then it becomes ques- tary lithologies (Figs. 3 and 5; Sukamto, 1975; Van tionable whether western, central and parts of the Leeuwen, 1981). However, given the very different Southeast Arm of Sulawesi were already juxtaposed lithologies and geochemistry of the igneous rocks by the Tertiary. Alternatively, these Tertiary dates the eastern part of the North Arm is now regarded may be deformational ages related to collision and as a separate tectonic province from the South Arm accretion of material onto eastern Sulawesi (PolveÂet and the neck of the North Arm (Van Leeuwen et al., al., 1997). Central and part of the Southeast Arm of 1994; see below). Central Sulawesi and parts of the Sulawesi have been attached to western Sulawesi in Southeast Arm of Sulawesi are composed of sheared the reconstructions shown, although these may need metamorphic rocks and in the east a highly tectonised re®nement as further data becomes available. meÂlange complex is present, together comprising the The East Sulawesi Ophiolite consists of a full Central Sulawesi Metamorphic Belt (Sukamto, 1975; suite of ophiolite lithologies, tectonically interca- Hamilton, 1979; Parkinson, 1991). Similarities be- lated with Cretaceous or Mesozoic pelagic sedimen- tween the pre-Tertiary rocks and a few potassium± tary rocks. Metamorphic ages (28±32 Ma; Parkinson, argon dates from some of the metamorphic rocks have 1991, 1998) from rocks overthrust by the East Su- been used to suggest that these regions, which in- lawesi Ophiolite suggest emplacement of this ophi- clude microcontinental fragments, had been accreted olite sequence occurred during or after the middle onto the eastern margin of Sundaland before the Ter- to late Oligocene. Palaeomagnetic data (Mubroto et tiary (Sukamto, 1975; Hasan, 1991; Parkinson, 1991; al., 1994), together with geochemistry and ®eld re- Parkinson et al., 1998; Wakita et al., 1994). However, lationships, have been used to infer that at least part data from the Central Sulawesi Metamorphic Belt, of the East Sulawesi Ophiolite formed further to the particularly from the Southeast Arm, is sparse, and the south in a back-arc setting (Fig. 3; Parkinson, 1991). timing of accretion of this area is poorly constrained. In comparison, a single back-arc basin origin for the The Tertiary stratigraphy of western Sulawesi is simi- East Sulawesi Ophiolite, the Palaeogene Tinombo± lar to that of eastern Kalimantan and the East Java Sea Labuanaki Formations of the North Arm of Sulawesi because the whole area had begun to subside by the and the Celebes Sea have been suggested on the basis middle Eocene and a widespread basin formed (Van of geochemical similarities (Monnier et al., 1995). de Weerd and Armin, 1992). Cenomanian to early Oligocene ages have been ob- The eastern side of the South Arm (Lamasi Vol- tained from ma®c rocks in the East Arm, suggesting canics and Kalamiseng Formation) and much of that the East Sulawesi Ophiolite may be composite in the eastern parts of the East and Southeast Arms nature (Parkinson, 1991). On the reconstructions, the of Sulawesi are composed of tectonically interca- back-arc basin in which the East Sulawesi Ophiolite, lated marine sedimentary rocks and ma®c and ul- and other possibly related oceanic fragments, may trama®c igneous rocks interpreted as an ophiolitic have formed, are not shown due to the con¯icting sequence (Sukamto, 1975; Silver et al., 1978; Yu- theories on their origin. However, if the Paleogene wono et al., 1987; Simandjuntak, 1990; Parkinson, igneous lithologies on the North Arm of Sulawesi 1991; Bergman et al., 1996). A somewhat confusing were generated in a deep marine setting rather than array of Cretaceous to Miocene K±Ar and Ar±Ar as a subduction related arc, the occurrence of a chain dates have been obtained from the ma®c and ul- of volcanic islands in northern Sulawesi would then trama®c rocks in eastern South Sulawesi (Yuwono be questionable. et al., 1987; Bergman et al., 1996). If the Tertiary On the islands of Buton±Tukang Besi and ages represent emplacement ages of this ophiolite se- Banggai±Sula, metamorphic and igneous litholo-

Fig. 4. Simpli®ed Cenozoic stratigraphic correlation in Borneo (after references given in text). Abbreviations for units are: SI D Sintang Intrusives; BB D Batu Baleh Limestone member; BA D Batu Ayau Formation; BK D Batu Kelau; RM D Ritan Member; UTF D Upper Tanjung Formation; LTF D Lower Tanjung Formation; T D Tabul; ML D Meliat Limestone; MS D Meliat Sandstone; L D Latih; TF D Togopi Formation; TK D Tukau; LB D Libong; TJ D Tanjong; SB D S. Banggai; S D Setap Shales; K D Kalumpang; GL D Gomantong Limestone. 312 M.E.J. Wilson, S.J. Moss / Palaeogeography, Palaeoclimatology, Palaeoecology 145 (1999) 303±337 M.E.J. Wilson, S.J. Moss / Palaeogeography, Palaeoclimatology, Palaeoecology 145 (1999) 303±337 313 gies of continental origin are exposed or are 4.1. Eocene (Figs. 6 and 7) thought to underlie shallow and deep marine sed- iments of Palaeozoic and Mesozoic ages, respec- A land connection between southern Borneo and tively. The Palaeozoic lithologies are thought to have mainland Southeast Asia is inferred to have existed Australian±New Guinea af®nities, whereas deposi- during the Eocene (Pupilli, 1973) and may have tion of shallow and deep marine sedimentary litholo- been present since the Jurassic (Lloyd, 1978). A thin gies is inferred during rifting and drifting of the frag- cover (<300 m) of Quaternary sediments is reported ments in the Mesozoic (Audley-Charles et al., 1988; to overlie pre-Tertiary rocks on the Sunda Shelf Hamilton, 1979; Pigram and Panggabean, 1984; Gar- (Ben-Avraham and Emery, 1973). However, since rard et al., 1988). Buton is thought to have collided few wells penetrate the succession on the Sunda with eastern Sulawesi during the early (Davidson, Shelf only a limited amount of geological informa- 1991) or middle Miocene (Smith and Silver, 1991), tion is available. Although a land area is inferred for whereas latest Miocene or early Pliocene collision this area throughout much of the Tertiary, it is possi- with the East Arm of Sulawesi is inferred for Bang- ble that marine sediments deposited during possible gai Sula (Garrard et al., 1988; Smith and Silver, transgressions of this region may have been removed 1991). Fortuin et al. (1990) and Davidson (1991) by later erosion. suggested that Tukang Besi was a separate micro- During the late Cretaceous to late Paleocene= continental block, which was accreted to Buton in Eocene, turbidites and other deep water sediments the Plio=Pleistocene, although not all authors recog- of the Rajang Group, Belaga, Mulu, Kelalan, East nise this as a separate microcontinental fragment Crocker Formations and parts of the upper Em- (Smith and Silver, 1991). baluh Group were deposited in deep marine basins in Sabah, Sarawak and northern Kalimantan (Liechti, 1960; Tate, 1991; Moss, 1998). Fluvial=marginal 4. Palaeogeographic evolution marine sands of the Kayan Sandstone Formation from southern Sarawak have been variously dated as A series of palaeogeographic maps for intervals Late Cretaceous to Tertiary, although structural and between the middle Eocene and the present day are stratigraphic relationships suggest that the ages may presented as Figs. 6±11. The palaeoenvironmental vary across Sarawak (Tate, 1991). Therefore these elements distinguished are land areas, including low sandstones may in part represent the lateral terres- lying regions of ¯uvial deposition, major river sys- trial and marginal marine equivalents to the deep tems and marginal marine=deltaic systems, as well marine sediments to the north. The sediments for as regions of more mountainous topography. Areas these shallow and deep marine clastics in northern of shallow water and deeper water ®ne grained and Borneo may have been supplied via river systems coarser redeposited clastic and carbonate deposits from Indochina. The upper Cretaceous and lowest were mapped. Volcanic activity, subdivided into ar- Palaeogene sediments were deformed and uplifted eas of inferred subaerial and submarine volcanism, in the `Sarawak Orogeny', and are unconformably is also shown on the reconstructions. The outlines overlain by shallow and deep marine sediments of the present day coastlines are shown on the re- of middle to late Eocene age, such as the Tatau, constructions for reference. Stratigraphic correlation Silantek and Melinau Formations in Sarawak and charts for Borneo and Sulawesi are shown as Figs. 4 the middle Eocene Kiham Haloq Sandstone Forma- and 5, respectively. tion in Kalimantan (BeÂnard et al., 1990; Hutchison, 1996a).

Fig. 5. Simpli®ed Cenozoic stratigraphic correlation in Sulawesi (after references given in text). Abbreviations for units are: S=PVD Soppeng=Parepare Volcanics; RL D Ratatokok Limestone; BD D Bone Diorite; SL D Salayar Limestone; WF D Walanae Formation; TL D Tacipi Limestone; BF D Bone Formation; TL D Tonasa Limestone; PU D Puna Formation; PO D Poso Formation; UPL D Upper Platform Limestone; LPL D Lower Platform Limestone. 314 M.E.J. Wilson, S.J. Moss / Palaeogeography, Palaeoclimatology, Palaeoecology 145 (1999) 303±337

Fig. 6. Palaeogeographic map for 50 Ma, early Eocene. A key to the environments is shown. Some place names are shown for reference. Rivers are shown schematically on all the palaeogeographic maps. M.E.J. Wilson, S.J. Moss / Palaeogeography, Palaeoclimatology, Palaeoecology 145 (1999) 303±337 315

Fig. 7. Palaeogeographic map for 42 Ma, middle Eocene. A key to the environments is shown in Fig. 6. 316 M.E.J. Wilson, S.J. Moss / Palaeogeography, Palaeoclimatology, Palaeoecology 145 (1999) 303±337

Cretaceous dates from schists in the basement line (Priadi et al., 1994), and are associated with complexes in Sulawesi suggest that western and later diorite, quartz diorite and granodiorite intru- central Sulawesi had been accreted onto southern sives (T.M. van Leeuwen, pers. commun., 1998). Borneo before the Tertiary (Sukamto, 1975; Parkin- Although Polve et al. (1997) suggested a back-arc son, 1991; Wakita et al., 1996). Outcrops of schists, setting for this area during the Eocene based on three gneisses and marbles, of unknown age, also occur dyke samples only. Along the eastern part of the in the Southeast Arm of Sulawesi, the island of North Arm volcanic rocks with bimodal associations Kabaena and the western part of the North Arm of of basalt±basaltic andesite and rhyolite dominate and Sulawesi. These areas and the South Arm of Su- are intercalated with pelagic limestones and cherts lawesi are regarded as a region of microcontinental with a few middle Eocene to lower Miocene nan- material and may have formed a contiguous land area nofossil dates (T.M. van Leeuwen, pers. commun., during the early Palaeogene as shown on the recon- 1998). Gabbros and diorites intrude the successions structions. However, it is stressed that data from this and the igneous lithologies are tholeitic and `MORB- region, particularly the Southeast Arm of Sulawesi, like' with a slight negative Nb±Ta anomaly and is extremely limited and that as more data becomes their geochemistry suggests a back-arc origin. The available the interpretations may change. Much of Palaeogene igneous lithologies in the neck of the mainland Southeast Asia, southern Borneo and west- North Arm have similarities with those in the rest ern Sulawesi appear to have been emergent during of western Sulawesi and may be subduction related the Paleocene and the early Eocene, with a distinct (Priadi et al., 1994), whereas an ophiolitic origin or lack of reliably dated sedimentary rocks recorded early stages of a volcanic arc have been inferred for from these periods. the eastern part of the North Arm (Carlile et al., Geochemistry, K±Ar and zircon ®ssion-track dat- 1990) ing of calc-alkaline rocks from the Langi Formation There was widespread formation of basins around (63 š 2.2 Ma; Sukamto, 1975 and 58.5 Ma; Van the margins of Sundaland by middle Eocene times. Leeuwen, 1981) and dating of interbedded sediments Much of eastern Borneo, western Sulawesi, the (Eocene=Oligocene foraminifera from the Langi and Makassar Straits and the East Java Sea was a re- Salo Kalupang Formations) in eastern South Su- gion of middle to late Eocene extension and sed- lawesi suggests that a volcanic arc occurred in this imentation. Depositional environments varied both area during the Palaeogene (Sukamto, 1975; Van temporally and spatially between ¯uvial, deltaic, Leeuwen, 1981; Sukamto and Supriatna, 1982). The shallow marine clastic and carbonate shelves and calc-alkaline nature and enrichment of light rare areas of deeper water sedimentation. Evidence for earth elements indicates that the volcanics were sub- Eocene extension, block-faulting and subsidence are duction related (Yuwono et al., 1985), probably from seen on seismic lines crossing the Makassar Straits a W-dipping subduction zone (Van Leeuwen, 1981). (Burollet and Salle, 1981; Situmorang, 1982; Gun- Palaeogene volcanics, volcaniclastic and sedimen- toro, 1995; Bergman et al., 1996) and this was the tary lithologies of the Tinombo Formation also occur time when the land connection between Borneo and in west-central Sulawesi and on the North Arm. Sulawesi was severed. The marginal oceanic basin However, the Tinombo Formation has very differ- of the Celebes Sea had begun to form in the middle ent characteristics in the neck of the North Arm Eocene (Weissel, 1980; Rangin and Silver, 1991) compared with the eastern part of the North Arm, in- and probably in¯uenced basin initiation in Borneo dicating very different origins for these areas. In the and Sulawesi (Hall, 1996, Moss et al., 1997). Basin neck, sedimentary lithologies dominate and include formation was partly contemporaneous with Eocene localised shallow marine limestones of middle and rhyolitic volcanism (50±45 Ma), and ash-falls and late Eocene ages, shales and turbidites, of greywacke lava ¯ows crop out in the Tarakan (Netherwood and composition containing clasts derived from conti- Wight, 1992) and Kutai Basins (Van Leeuwen et al., nental material (Van Leeuwen et al., 1994). Vol- 1990; Heryanto et al., 1993; Suwarna et al., 1993; canic suites consist of basalt±andesite±dacite, which Moss et al., 1997). Similar volcanism also occurred are dominantly volcanic arc tholeitic and calcalka- along the southern margin of the Mangkalihat Penin- M.E.J. Wilson, S.J. Moss / Palaeogeography, Palaeoclimatology, Palaeoecology 145 (1999) 303±337 317 sula (Sunaryo et al., 1988) and the in the Muller Tatau Formations were deposited under marginal ma- Mountains (Pieters et al., 1993b). rine to marine conditions (Liechti, 1960). The Upper In western Borneo, ¯uvial and lacustrine sedi- Eocene shallow marine carbonates of the Engkili For- ments, such those forming the Ingar and Dangkan mation, deposited in the Lubok region of southwest- Formations, were deposited throughout much of the ern Sarawak unconformably overlie the Lubok Antu Eocene in elongate depocentres of the Melawi± melange (Haile, 1998). Shallow marine carbonates of Ketungau±Mandai Basins (Fig. 2). It is inferred that the Melinau Limestone in northeastern Sarawak, are sediment deposited in these areas was supplied by late Eocene to middle Miocene (Adams, 1965), and rivers ¯owing from the south (Schwaner Mountains probably developed in areas of antecedent topography area) or west from Indochina, since marine depocen- isolated from clastic input. tres were present to the north and east and are un- likely to have been a sediment source. Fluvial and 4.2. Oligocene (Fig. 8) marginal marine sediments were also deposited in southeastern Borneo, although by late Eocene times A land connection between Borneo and Indochina shallow and deep marine clastic and carbonate sed- is still inferred for the Oligocene (Pupilli, 1973; imentation also occurred. Marginal marine litholo- Lloyd, 1978). Turbiditic sediments and shales of gies with coals and intercalations of volcanic rocks of the Temburong, Setap Shale and West Crocker For- the Sembukung Formation occur with the Tarakan± mations were deposited in Sarawak and Sabah in Muara depocentres, although shallow and deeper wa- deep marine basins. These may have been fed large ter carbonate deposition was common by the Late quantities of sediment by river systems originat- Eocene on the Mangkalihat Peninsula (Wilson et al., ing in the Central Kalimantan Ranges or Indochina. 1999). By middle to late Eocene times large parts of These deep marine successions pass laterally into the Kutai Basin (NP17±19; Moss and Finch, 1998) shallow marine sediments (Temburong and Setap and neighbouring western Sulawesi (Wilson, 1995) Formations) in Brunei (Tate, 1994) and deltaic sedi- were areas of deep and shallow open oceanic sed- mentation occurred around the margins of the basin imentation (Wilson, 1995; Calvert, pers. commun., in Sabah and Sarawak. Several areas of shallow ma- 1998) and a deep marine setting is inferred for much rine carbonate deposition (Melinau, Selidong and of the North and South Makassar Basins. Around Keramit Formations) were present in the Sabah± the margins of this deep basin, in the Kutai Basin, Sarawak region throughout most of the Oligocene, the northern part of the Tarakan Basin and west- although deposition was not continuous (Adams, ern Sulawesi, Upper Eocene deltaic sands, coals and 1965). The Sarawak Basin was progressively in®lled some shallow marine clastics and carbonates were with argillaceous sediments during the Oligocene deposited (Kusuma and Darin, 1989; Van de Weerd (Doust, 1981). and Armin, 1992; Cof®eld et al., 1993; Moss et al., In the North and South Makassar Basins, deep 1997; Moss and Chambers, 1999). In the western part marine sedimentation in uniformly subsiding basins of the South Arm of Sulawesi, marginal marine clas- is inferred for the Oligocene based on ¯at lying re- tics and coals of the Malawa=Toraja Formation are ¯ectors seen on seismic (Situmorang, 1982; Guntoro, conformably overlain by a thick sequence of shallow 1995). However, in other parts of the basin, partic- marine carbonates of the Tonasa Formation, the base ularly along the eastern margin of the Paternoster of which is lower=middle Eocene to upper Eocene Platform, seismic and borehole data suggests active (Crotty and Engelhardt, 1993; Wilson and Bosence, extensional faulting may have continued sporadi- 1997). By late Eocene times shallow marine carbon- cally through the Oligocene, and possibly into the ate sedimentation had been established over much of Miocene (Situmorang, 1982; Guntoro, 1995; Wilson southern Sulawesi (the Tonasa and Makale Forma- and Bosence, 1996). Oligocene deep marine sedi- tions) although some areas were separated by deep mentation also occurred in much of the Kutai Basin marine basins (Wilson and Bosence, 1996; Wilson et (Moss et al., 1997) and in some areas of west-cen- al., 1999). In Sarawak and Brunei dominantly argilla- tral Sulawesi (Wilson, 1995). In the Tarakan±Muara ceous sediments of units such as the Silantek and area, the Mangkalihat Peninsula, Barito Basin, off- 318 M.E.J. Wilson, S.J. Moss / Palaeogeography, Palaeoclimatology, Palaeoecology 145 (1999) 303±337

Fig. 8. Palaeogeographic map for 34 Ma, early Oligocene. A key to the environments is shown in Fig. 6. shore southern Barito and in South Sulawesi ex- volcaniclastic sediments is recorded in west-central tensive areas of shallow water carbonate platforms Sulawesi. developed or continued to accumulate sediment dur- The depocentre of the mainly ¯uviatile west Kali- ing the Oligocene, whilst deeper water marls were mantan Basin (Melawi±Ketungau±Mandai Basins) deposited in adjacent areas (Bishop, 1980; Van de had begun to diminish in size or had already been Weerd et al., 1987; Bransden and Matthews, 1992; in®lled by the early Oligocene. Fission track dating Netherwood and Wight, 1992; Saller et al., 1992, of derived apatite grains and seismic data suggest 1993; Van de Weerd and Armin, 1992; Supriatna et that the Semitau ridge began to rise in the early al., 1993; Wilson, 1995; Wilson et al., 1999). A num- Oligocene (Moss et al., 1998), and this uplift would ber of Oligocene unconformities in these areas have have favoured erosion rather than deposition in this been related to local tectonics, possibly enhanced by area. Deltaic and pro-delta environments appeared eustatic sea-level variations (Netherwood and Wight, in the western part of the Kutai Basin towards the 1992; Saller et al., 1993; Satyana, 1995). An input of end of the Oligocene (Van de Weerd and Armin, M.E.J. Wilson, S.J. Moss / Palaeogeography, Palaeoclimatology, Palaeoecology 145 (1999) 303±337 319

1992; Tanean et al., 1996; Moss et al., 1997). This is 4.3. Miocene (Figs. 9 and 10) thought to be related to uplift of the central ranges of Borneo towards the end of the Oligocene, and the On the east side of Borneo, particularly in the erosion of these areas supplied sediment eastwards Tarakan±Muara and Barito basinal areas, a switch towards the Makassar Straits (Moss et al., 1998). in sedimentation style from extensive carbonate Tectonically intercalated ultrama®c and ma®c shelves to deltaic deposition and progradation oc- rocks and intercalated marine sedimentary rocks curred during the Miocene (Achmad and Samuel, comprising much of the East and Southeast Arms 1984; Netherwood and Wight, 1992; Van de Weerd of Sulawesi have been interpreted as part of an ophi- and Armin, 1992; Siemers et al., 1992; Carter and olite sequence (Simandjuntak, 1986). Metamorphic Morley, 1996; Stuart et al., 1996). The predomi- ages of between 28 and 32 Ma, obtained by K±Ar nance of deltaic sedimentation around the northern analysis, from the metamorphic sole at the base of and eastern parts of Borneo, particularly in the ex- the East Sulawesi Ophiolite suggest the ophiolitic tremely deep Kutai Basin, suggests that most of the suite was emplaced during or after the latest early major river systems were draining into these areas. or late Oligocene (Parkinson, 1991, 1998). Prior to Abundant detritus was supplied from the uplift and the emplacement of the East Sulawesi Ophiolite onto denudation of the centre of the island and coeval western Sulawesi, the ophiolite succession would volcanism (Tanean et al., 1996; Moss et al., 1997, have formed as part of the ocean crust in a deep 1998). By the end of the Miocene, the drainage marine environment, with a possible back-arc or system within Borneo was similar to the present- supra-subduction zone origin (Girardeau et al., 1995; day. The Mahakam delta had prograded to near its Monnier et al., 1995; Parkinson, 1998). The progres- present-day position by the middle Miocene, and sive emplacement of the ophiolitic material would siliciclastic marginal marine and deltaic deposition have resulted in the development of more extensive predominated in this area (Addison et al., 1983; Land land areas in Sulawesi. and Jones, 1987). The Makassar Straits was still a The microcontinental blocks of Banggai±Sula, major deep water basin separating Sulawesi from Buton and Tukang Besi although drifting westwards Kalimantan, although as the land area increased in during the Oligocene, had yet to be accreted onto eastern Borneo, due to the progradation of deltas, Sulawesi. Permo-Triassic schists and slates of con- the distance across this seaway was progressively tinental origin are overlain by Upper Triassic to reduced. Jurassic shallow marine clastics and carbonates and In northern Borneo, the lower Miocene Melin- deep marine Jurassic=Cretaceous shales, which are gan delta, middle to upper Miocene Champion delta thought to have been deposited during rifting and and upper Miocene to Quaternary Baram deltas pro- drifting away from the Australian continent (Gar- graded towards the northwest (Koopman, 1996). In rard et al., 1988; Davidson, 1991; Smith and Silver, Sabah, shallow marine to marginal marine sediments 1991). Eocene to Miocene shallow marine clastics were deposited (Tjia et al., 1990; Clennell, 1992). and carbonates of the Salodik and Pancoran For- Several extensive unconformities occur within shal- mations unconformably overlie older lithologies on low marine to deltaic Neogene successions in the Banggai±Sula (Garrard et al., 1988). In the Buton offshore West Sabah region. These resulted from and Tukang Besi areas, deep water carbonates of the faulting and folding, and the middle and upper Tobelo Formation were deposited between the Late Miocene unconformities are known as the `Deep Cretaceous and the late Eocene or early Oligocene and Shallow Regional Unconformities', respectively (Smith and Silver, 1991; Davidson, 1991). There- (Bol and Van Hoorn, 1980; Levell, 1987). During the fore, although these microcontinental blocks would late Miocene, the northern Borneo coastline changed not have been land areas during the rifting and drift- from having a N±S orientation to a SW±NE orienta- ing phase in the later part of the Mesozoic, some tion, similar to today. A large area of shallow marine areas were regions of shallow marine sedimentation carbonate deposition developed during the middle to and may have become emergent during the Eocene late Miocene in the Luconia Shoals area, which was and Oligocene. suf®ciently distant from areas of coastal siliciclastic 320 M.E.J. Wilson, S.J. Moss / Palaeogeography, Palaeoclimatology, Palaeoecology 145 (1999) 303±337

Fig. 9. Palaeogeographic map for 21 Ma, Early Miocene. A key to the environments is shown in Fig. 6. deposition in Sarawak (Epting, 1980; Doust, 1981; Hutchison, 1996a; Tanean et al., 1996; Moss et al., Agostinelli et al., 1990; Rice-Oxley, 1991). 1997, 1998). South-dipping subduction under north- Volcanics and associated intrusives of the upper western Borneo has been inferred as the reason for Oligocene to Lower Miocene Sintang Igneous Suite this magmatism, although an alternative model of crop out sporadically over much of central Borneo crustal thickening and sub-crustal melting has also (Bergman et al., 1987; Pieters and Supriatna, 1990; been suggested (Bergman et al., 1987; Pieters et Pieters et al., 1993a,b, 1993c; Heryanto et al., 1993; al., 1993a,b, 1993c; Tanean et al., 1996). Volcanic M.E.J. Wilson, S.J. Moss / Palaeogeography, Palaeoclimatology, Palaeoecology 145 (1999) 303±337 321

Fig. 10. Palaeogeographic map for 8 Ma, late Miocene. A key to the environments is shown in Fig. 6. arc activity occurred along the Cagayan and Sulu (Polve et al., 1997). Shallow marine carbonates are ridges during the Miocene and Plio-Pleistocene, re- interbedded with these igneous rocks and volcanic spectively, and probably resulted in emergent chains islands are inferred to have been emergent. During of volcanic islands (Rangin and Silver, 1991). Ig- the middle Miocene to late Miocene=early Pliocene, neous activity associated with these arcs may have a volcanic arc with abundant intrusives and extru- extended into Sabah and the Philippines, although sives developed along the length of western Sulawesi the dating of igneous rocks from these areas is older (Yuwono et al., 1987; Bergman et al., 1996). These than from the arcs (Rangin and Silver, 1991). igneous lithologies vary from calc-alkaline to mildly In South Sulawesi, shallow marine carbonate de- alkalic, potassic, and shosonitic felsic and ma®c position continued until the middle Miocene, on high composition. This bimodal composition has been blocks, surrounded by deep marine sedimentation related to lithospheric thickening, resulting from col- (Cof®eld et al., 1993; Wilson et al., 1999). The East lisions onto eastern Sulawesi and the subsequent Sulawesi Ophiolite had been or was being accreted melting of oceanic and continental crust (Cof®eld et onto western Sulawesi, and it is inferred that land al., 1993; Bergman et al., 1996). areas became emergent in central Sulawesi during The microcontinental blocks of Banggai±Sula and the Miocene as a result of this collision. In the Buton Tukang Besi were accreted onto eastern Su- North Arm of Sulawesi magmatic eruptions during lawesi during the Miocene or earliest Pliocene. The the Oligocene to Miocene produced successively is- inferred timing of collision of the various fragments land arc tholeiites and calc-alkaline igneous rocks onto eastern Sulawesi varies depending on the au- 322 M.E.J. Wilson, S.J. Moss / Palaeogeography, Palaeoclimatology, Palaeoecology 145 (1999) 303±337 thor. On Buton, obduction of ophiolitic material (Garrard et al., 1988; Davies, 1990). These may have and the erosion of upthrusted pre-Miocene strata become emergent during the Tertiary and more ex- and their subsequent reworking into clastic deposits tensive land areas would have formed after collision. of the Tondo Formation has been related to early (Fortuin et al., 1990; Davidson, 1991) or middle 4.4. Pliocene±Recent (Fig. 11) (Smith and Silver, 1991) Miocene collision of Buton with the Southeast Arm of Sulawesi=Muna. Prior to The coastlines of Borneo and Sulawesi, by the this collision, deep marine sediments were deposited Pliocene, were similar to the present day. Ma- on Buton, although uplift and thrusting associated jor areas of shallow water carbonates persisted on with accretion (Davidson, 1991) may have created the east and west sides of the Makassar Straits. emergent land areas in the middle Miocene. Lat- Deltaic and marginal marine sedimentation prevailed est Miocene to early Pliocene collision of Banggai± around much of the coast of Borneo. The Mahakam Sula with eastern Sulawesi has been inferred from river carries a large sediment volume which is de- the timing of compressional structures and sedimen- posited mainly in the delta (estimated at 8.106 m3 tological constraints (Garrard et al., 1988, Davies, yr1, Allen, 1996) and deltaic progradation occurred 1990). Eocene to middle Miocene limestones are throughout the Pliocene and continues to the present present on Banggai Sula indicating shallow water day. Similarly, delta progradation on the Sarawak depositional environments existed prior to collision and Brunei side of Borneo has been rapid and

Fig. 11. Palaeogeographic map for 4 Ma, early Pliocene. A key to the environments is shown in Fig. 6. M.E.J. Wilson, S.J. Moss / Palaeogeography, Palaeoclimatology, Palaeoecology 145 (1999) 303±337 323 involved large quantities of sediment. The Rajang and subsidence in other areas. The evolution of the delta, for example, has an average discharge of 3550 deep gulf separating the South and Southeast Arms m3=s (Staub and Esterle, 1994). During the latest of Sulawesi, known as Bone Bay, is inferred to Miocene or Pliocene, Borneo lost its land connection have developed as an extensional feature in the late with mainland Indochina (Lloyd, 1978). Possible Oligocene (Davies, 1992). Davies (1992) and Gun- reasons for this include global sea-level changes and toro (1995) suggested from seismic data that the the end of late Miocene glaciation and=or plate read- form of Bone Bay was then further modi®ed during justments. The present-day Karimata Strait probably the Miocene=Pliocene by transpressive and transten- did not form until 7000 years ago, as suggested by sional movements. Historic legends and the nature the presence of a drowned Pleistocene river drainage of Quaternary sediments suggest that until quite re- system on the Sunda Shelf, which is thought to cently a seaway separated the South Arm from the have developed during a relative sea-level lowstand rest of Sulawesi (Van Bemmelen, 1949; Sartono, (Umbgrove, 1938). 1982). The ®nal juxtaposition of fragments that com- Basaltic to trachyandesitic volcanics of the Met- prise Sulawesi occurred between the Pliocene and alung Suite or Plateau Volcanics formed shield vol- the present day. Although most authors infer that in- canoes and lava ®elds in central Borneo in the latest ternal rotation and juxtaposition was achieved via a Miocene to Pleistocene (Moss et al., 1997, 1998). system of linked strike-slip faults and thrusts, includ- Igneous activity continued in western Sulawesi until ing the Lawanopo, Matano and Palu faults (Fig. 3), the Pliocene and Pleistocene and is similar in nature the linkage and displacements along faults is still to late Miocene volcanism in the same area (Yuwono contentious. The Pliocene reconstruction shown is et al., 1987; Bergman et al., 1996). On the North based on matching palaeoenvironments and assum- Arm of Sulawesi, Miocene to Pliocene calk-alka- ing reasonable strike slip displacements along ma- line volcanism, producing dominantly andesitic and jor faults and some internal deformation of blocks some rhyodacitic rocks, is related to S-dipping sub- within Sulawesi. Continued deformation of Sulawesi duction of the Celebes Sea oceanic crust under the has been related to transpression due to collision North Arm (Carlile et al., 1990). A string of active of fragments onto eastern Sulawesi and continued Quaternary to Recent volcanoes, formed of andesitic subduction east of Sulawesi. Indeed, intensely kars- to dacitic pyroclastics, dominate the Sangihe Islands ti®ed upper Pliocene to Pleistocene limestones of the and the eastern part of the Minahasa region, and Wapulaka Formation, which unconformably over- are related to W-dipping subduction under this area lie older formations in Tukang Besi=Buton, have (Carlile et al., 1990). been interpreted as syntectonic platform carbonates deposited on fault-blocks during the collision of Tukang Besi with Buton (Fortuin et al., 1990; David- 5. Natural resources son, 1991). Although, Smith and Silver (1991) con- sidered Buton and Tukang Besi to be part of a single Borneo and Sulawesi are areas of frontier explo- block, which was accreted by the middle Miocene. ration, with considerable economic potential. Proven The transpressional regime during the Neogene and and potential hydrocarbon reserves occur in the thick Quaternary resulted in uplift of extensive areas in Tertiary sedimentary sequences (Fig. 12), construc- Sulawesi and caused the rapid uplift of a number tion materials are abundant and a number of different of high mountain areas, particularly in central Su- mineral deposits occur associated mostly with ig- lawesi. K±Ar and ®ssion track geochronology data neous rocks (Fig. 13). Active volcanic areas with the suggest that between 2 and 5 Ma rapid uplift rates potential for harnessing geothermal energy occur in of 200±700 m Ma1, typical of fold and thrust belts, the North Arm of Sulawesi and northern Borneo. occurred in central Sulawesi (Bergman et al., 1996). This section provides a review of known resources of The transpressive regime operating in Sulawesi these two islands, relating them to spatial and tem- during the Neogene and Quaternary, as well as caus- poral palaeogeographic variations. In the past eco- ing uplift of certain areas, also resulted in extension nomic deposits in the area have mostly either been 324 M.E.J. Wilson, S.J. Moss / Palaeogeography, Palaeoclimatology, Palaeoecology 145 (1999) 303±337 M.E.J. Wilson, S.J. Moss / Palaeogeography, Palaeoclimatology, Palaeoecology 145 (1999) 303±337 325 discovered by enterprising local people or by explo- basement. The Tertiary transgressive sequences ®ll- rationists and prospectors using standard geological ing the extensive basins in Borneo, Sulawesi and techniques. However, palaeogeographic reconstruc- the surrounding seas (Fig. 12) are commonly com- tions have become a recognised and increasingly posed of marginal marine clastics and coals passing important tool in the future exploration for natural upwards into shallow marine carbonates or deeper reserves and their potential usage is also reviewed. marine clastics (Figs. 4 and 5). In western Sulawesi, Coals were deposited in western Sulawesi and the source for oil and gas with Type-II and -III kero- eastern Kalimantan during the Eocene as part of gens has been geochemically traced back to Eocene the syn-rift succession in the Tertiary depocentres. coals (Cof®eld et al., 1993) and to Neogene deltaic These coals are usually marginal-marine, although coals and shales in Borneo (Durand et al., 1988; some lacustrine coals have been identi®ed in south- Schiefelbein et al., 1997). In Borneo, thick Neogene eastern Kalimantan (Fig. 12). The thickness of coal deltaic sequences comprise major proven reserves beds is usually up to a few metres, although 8 and (James, 1984; Du Bois, 1985; Durand et al., 1988; 15 m thickness beds occur in southeastern Kaliman- Courteney, 1995; Sandal, 1996; Graves and Swauger, tan and the Lariang±Karama Basins in Sulawesi, 1997; Schreurs, 1997), with 2.5 billion barrels of oil respectively (Van Bemmelen, 1949; S. Calvert, pers. and 28 TCF of gas alone discovered to date in the commun.). Although large, economically viable coal Kutai Basin (Paterson et al., 1997). Magmatism and ®elds occur in southern Kalimantan (Van Leeuwen, orogenesis during the late Cenozoic facilitated hy- 1994), in most other areas of Borneo and Sulawesi drocarbon generation in western Sulawesi (Cof®eld the Palaeogene coals are mined on a local scale. et al., 1993; Wilson et al., 1997). In both areas clas- In comparison, numerous economically viable coal tics and carbonates with moderate to high poroperms seams occur in the Neogene successions, often in comprise the reservoirs. Hydrocarbon traps may be deltaic sequences, in Sabah, Sarawak, eastern and either stratigraphic, such as carbonate buildups (Ept- southeastern Kalimantan (Fig. 12; Pei, 1992; Van ing, 1980; Grainge and Davies, 1983; Ascaria et Leeuwen, 1994; Hutchison, 1996b). An example of al., 1997) or deepwater clastic fans (Malecek et these are middle Miocene coals near Samarinda in al., 1993), or structural, as in thrusted anticlines the Kutai Basin where some 1000 Mt of resources (Cof®eld et al., 1993; Paterson et al., 1997). have been recognised in some 43 seams ranging be- In Sulawesi, seeps with heavy oils occur on Buton tween 1.5 and 13 m thick (Land and Jones, 1987). island and have been sourced from Triassic bitu- In Sabah and Sarawak the Meliau and Merit Pila minous marine shales and limestones with Type-II coal ®elds are estimated to have 400 and 200 Mt kerogens (Davidson, 1991). Oil generation has been of reserves, respectively (Pei, 1992). The coal rank related to burial due to thrusting during the late ranges from lignite-A to high volatile C bituminous Miocene (Davidson, 1991). The primary and sec- and are generally low ash, high moisture and low sul- ondary reservoir units are clastics and carbonates phur. Palaeogene coals have higher ash and sulphur of the Tondo and Sampolakosa Formations, respec- contents and lower moisture contents than Neogene tively, and both structural and stratigraphic traps coals due to their different respective environments have been identi®ed (Davidson, 1991). Gas reser- of formation in swampy and ¯uvio-deltaic areas (Van voirs have also been discovered in Miocene carbon- Leeuwen, 1994). ates in the Tomori area on the East Arm of Sulawesi, Hydrocarbon exploration in Southeast Asia is for adjacent to the islands of Banggai±Sula (Davies, the most part restricted to the Tertiary basins and the 1990). Tertiary coals or organic rich carbonates may pre-Tertiary is mostly considered as economic base- form the source for the hydrocarbons and similar to ment (Hutchison, 1996b), although in the Tanjung Buton, thrust loading is thought to have resulted in ®eld, hydrocarbons do occur in fractured granitic generation of hydrocarbons (Davies, 1990).

Fig. 12. Simpli®ed geological map of Borneo and Sulawesi, showing Cenozoic sedimentary thicknesses, and peat, coal and hydrocarbon accumulations (after Hamilton, 1979; Hutchison, 1989; Moss and Chambers, 1999). 326 M.E.J. Wilson, S.J. Moss / Palaeogeography, Palaeoclimatology, Palaeoecology 145 (1999) 303±337 M.E.J. Wilson, S.J. Moss / Palaeogeography, Palaeoclimatology, Palaeoecology 145 (1999) 303±337 327

All the elements of a complete petroleum systems, Mineralisation is commonly associated with ig- consisting of source rock, carrier bed, reservoir, seal, neous intrusions or fractures in Borneo and Sulawesi trap, kitchen areas and charge timing are present in (Fig. 13). On both islands minerals such as gold, Borneo and Sulawesi (Van de Weerd and Armin, diamond and platinum have been reworked and now 1992; Cof®eld et al., 1993; Wilson et al., 1997). often occur as placer deposits. Chromite and nickel The actual occurrence of signi®cant hydrocarbons are associated with ultrama®c rocks in ophiolite critically depends on a number of additional factors successions in Sabah, the Meratus Mountains in Bor- including volume of source rock, focus of hydrocar- neo and the Southeast and South Arms of Sulawesi bon charge, diagenesis of carrier beds and reservoir, (Van Bemmelen, 1949; Hutchison, 1972, 1996b; Go- seal capacity and timing of migration of hydrocar- lightly, 1979; Van Leeuwen, 1994). In eastern Su- bons relative to the deposition of seal lithologies and lawesi, the Soroako and Pomalaa mines include con- trap formation. siderable reserves of nickel and have been mined Construction materials, including granites, gneis- since the 1970's (Van Leeuwen, 1994). Minerals as- ses, marbles, serpentinites, limestones, sands and sociated with volcanic or intrusive rocks in Sulawesi gravels, occur in Sulawesi and Kalimantan (Sukamto, and Kalimantan include gold, silver, copper, tour- 1973; Ratman, 1976; Madiadipoera, 1990). These are maline and molybdenum (Sukamto, 1973; Ratman, utilised locally for road building, producing house- 1976; Carlile et al., 1990; Kavalieris et al., 1990, hold items or house foundations. However, con- 1992; Van Leeuwen et al., 1990, 1994). The North struction materials are scarce in eastern Sarawak, Arm of Sulawesi is a major area of mineralisation Brunei, Sabah and some areas of eastern Kaliman- associated with igneous activity and the nature of the tan. Miocene±Pliocene microgranodiorites in Tawau mineralisation is varied. Styles of mineralisation in- are exported as far as Brunei (C.S. Hutchison, pers. clude igneous dome-related (Kavalieris et al., 1992), commun., 1998). East Kalimantan imports most of its mineralised breccia zones (Lubis et al., 1994), as road and building aggregate material from the Palu porphyry Cu±Au and epithermal Cu±Au±Ag min- region of Sulawesi, because of the lack of igneous eralisation often associated with diatremes (Perello, rocks in the developed parts of the province (T.M. 1994) or associated with long-lived volcanic cen- van Leeuwen, pers. comm., 1998). In the South Arm, tres (Carlile et al., 1990; Kavalieris et al., 1992). In the Tonasa-II limestone quarry, one of the largest in- the Ratatokok area gold occurs as sediment-hosted dustries in Sulawesi, produced 1,280,116 metric tons in karstic in®lls in the Ratatokok limestone, along of cement in 1992, which is exported throughout east- permeable zones at limestone±andesite contacts, as ern Indonesia and to adjacent countries (P.T. Semen vein ®lls and eluvial gold deposits related to residual Tonasa, 1992). Clay and sand needed in the cement quartz-clay breccias (Turner et al., 1994). Lead bear- making process is either quarried locally or shipped ing gossans, associated with the West Walanae Fault in from eastern Kalimantan. Smaller quarries also oc- Zone in South Sulawesi were investigated by PT Rio cur in South Sulawesi and eastern Kalimantan and the Tinto, but found to be non-economic (Van Leeuwen, limestone is used for a variety of purposes, including 1981). More signi®cant, albeit still small, base metal decorative facing stone, construction, lime for agri- occurrences are at Riam Kusik and Long Laai in cultural use and as a raw material for the pharmaceu- Borneo and Sangkaropi in Sulawesi (Van Leeuwen, tical industry. The thick sequence of carbonates from 1994). In Kalimantan, epithermal gold mineralisa- the Tonasa Formation in Sulawesi is best for these tion is common and includes the largest gold mine in purposes as it was deposited as an isolated platform Indonesia at Kelian located within the Kutai Basin. away from clastic input. Several of the mineralisation sites in Kalimantan

Fig. 13. Simpli®ed geological map of Borneo and Sulawesi highlighting areas of pre-Tertiary basement, ophiolitic successions, igneous lithologies and structures. Mineral occurrences and areas of volcanic activity and geothermal prospects are also shown (after Clarke, 1989; Van Leeuwen, 1994; Carlile and Mitchell, 1994; Hutchison, 1996b). Major and minor occurrences of minerals have not been differentiated, for this the reader is referred to the aforementioned references. 328 M.E.J. Wilson, S.J. Moss / Palaeogeography, Palaeoclimatology, Palaeoecology 145 (1999) 303±337 appear to be located upon linear NE±SW-structures for example Paleogene and Neogene coals in Bor- and often occur where these are intersected by NW± neo have very different characteristics due to their SE-trending structures. The mineralisation in Bor- ¯uviatile=marginal marine and deltaic settings re- neo is also commonly associated with volcanic and spectively. Another example of this is where very intrusive rocks of uppermost Oligocene to middle pure carbonates are needed for cement production or Miocene Sintang intrusives (Van Leeuwen et al., in the pharmaceutical industry. Isolated carbonates 1990; Felderhof et al., 1996). Gold and other min- platforms, which developed distally from any clastic erals such as antimony have also been produced or volcaniclastic input such as the Tonasa Formation economically from placer deposits and eluvial or in South Sulawesi, as identi®ed on palaeogeographic residual deposits associated with carbonates in Bor- maps, are most likely to have fewest impurities. In neo, particularly the Bau district (Wilford, 1955; situ mineral occurrences are commonly associated Hutchison, 1996b). Diamonds have also been found with certain rocks types, often igneous lithologies in as placer deposits in western and southern Kaliman- Borneo and Sulawesi, and=or structures active dur- tan and Sarawak, although the original source of the ing particular time periods. Combined plate tectonic diamonds has never been traced (Sikumbang, 1986; and palaeogeographic maps are useful for deducing Bergman et al., 1987; Hutchison, 1996b). the timing of emplacement or extrusion of igneous Hot springs are commonly reported in western material and variations in stress regimes through Sulawesi, particularly from the North Arm, associ- time, hence giving valuable information on the likely ated with areas of recent or active volcanic activity, timing of structures. or from along faults, such as those along the margins of the Palu Depression (Sukamto, 1973; Boedihardi et al., 1992). The Lahendong Geothermal Field is 6. Biogeographic implications located close to Menado in the centre of a small crater which formed during the Pliocene (Surach- Borneo and Sulawesi occur on either sides of man et al., 1987). Two water reservoirs have been Wallace's original faunal divide and are of prime identi®ed at depths of 400±900 m and 1500 m with importance to biogeographers. In general, the organ- respective acidic water temperatures of 260ëC and isms of Borneo show similarities with those of Asia 300±350ëC and development of a 55 MW power and other islands on the Sunda Shelf, whereas on plant was proposed for this area (Surachman et al., Sulawesi there is a particularly high degree of en- 1987). Geothermal prospecting has been undertaken demism, with the biota showing both an Asiatic and in an area where hot springs, seepages, mud pools Australian in¯uence (reviewed in: Whitmore, 1981, and steaming ground occur on the Semporna Penin- 1987; Whitten et al., 1987; and MacKinnon et al., sula in Sabah. These features are related to major 1996). Both Borneo and Sulawesi contain a variety fracture systems and are associated with Quaternary of habitats, including high, mountainous areas, lower dacites, tuffs and agglomerates (Siong et al., 1991). rolling topography and ¯at coastal plains. A complex As an aid to future exploration for natural re- interplay of factors, including physical differences in sources the palaeogeographic maps can be used in a environment (such as altitude, soil type and slope number of different ways, although it is stressed that all in¯uenced by local geology), local and regional palaeogeographic information must be used in com- variations in climate as well as regional geological bination with the full range of geological data. In the evolution of the area, will all in¯uence the nature and hydrocarbon industry comparing different palaeo- diversity of organisms found on these islands. Today geographic maps can help to identify temporal and the region has a tropical climate, although some ar- spatial changes in source rock, reservoir and sealing eas of Sulawesi may experience long dry periods and lithologies within a basin. Since these are integral a more monsoonal climate than areas in Borneo. parts of any petroleum system, palaeogeographic re- Important elements of the palaeogeographic re- constructions are routinely used in play and prospect constructions for biogeographers to consider are the scales of investigation. Palaeogeographic data can temporal and spatial extent of land areas and island be used to infer the nature of certain rock types; chains, the timing and nature of material accreted M.E.J. Wilson, S.J. Moss / Palaeogeography, Palaeoclimatology, Palaeoecology 145 (1999) 303±337 329 onto the margin of the Sundaland craton and the the interchange of biota during the later part of distribution of different environments through time the Tertiary, particularly during periods of relative and space. The main palaeogeographic changes in sea level lows when large areas of shallow marine the region of Borneo and Sulawesi and their impli- shelves may have become emergent. cations for biogeography are brie¯y outlined below ± Although Borneo and western Sulawesi remained and discussed in detail in Moss and Wilson (1998): in near tropical latitudes throughout the Tertiary, ± A continuous land connection between Borneo the wide variety of micro-environments shown and mainland Southeast Asia existed throughout on the palaeogeographic maps would have led much of the Tertiary and would have allowed the to niche partitioning. This may help to explain unhindered migration of terrestrial biota. the higher number of endemic species in Borneo ± Western Sulawesi had been accreted onto east- compared with Sumatra, which otherwise does ern Borneo by the Late Cretaceous and by the show a marked similarity in fauna and ¯ora with Early Eocene land areas were emergent in the Borneo. Schwaner Mountains, northwestern Kalimantan, the Mangkalihat Peninsula and parts of western Sulawesi. The dispersal of certain ¯ora and fauna 7. Plate tectonic reconstructions and further between Borneo and western Sulawesi could have work occurred at this time. ± Extension in the Makassar Straits region and the Although much of the tectonic evolution of Bor- formation of surrounding Tertiary basinal areas in neo and Sulawesi during the Cenozoic can be in- the Paleogene resulted in the progressive separa- ferred (above), the complex tectonic setting, inac- tion of locally emergent land or volcanic areas cessibility, and lack of detailed geological work in in western Sulawesi and Borneo and this isola- some areas may result in inaccurate, con¯icting or tion goes some way towards explaining the high confusing interpretations. During the compilation of degree of endemism on Sulawesi. geological and tectonic information in order to con- ± The East Sulawesi Ophiolite was accreted onto struct the palaeogeographic maps it became clear Sulawesi during or after the late Oligocene and that a number of key points concerning the geology resulted in the formation of more extensive land of Borneo and Sulawesi need to be resolved and areas in Sulawesi. Since the ophiolitic suite orig- require further study. These include: inally formed as part of the oceanic crust in a ± Whether Borneo and Sulawesi have rotated, and deep marine setting, it would not have acted as a if so which fragments and the direction, magni- potential raft for biota. tude, timing and causes of rotation. There is still ± Microcontinental fragments accreted onto eastern considerable controversy over the interpretations Sulawesi in the Miocene to Pleistocene may have of palaeomagnetic results, as to which palaeo- been emergent as they drifted towards Sulawesi magnetic results are meaningful and which repre- and comprised island hopping=rafting routes for sent local or regional rotations. Variable amounts biota of Australian af®nity. of counterclockwise rotation or no rotation have ± Island hopping routes for the dispersal of organ- variously been inferred for Borneo and South Su- isms to and from Borneo and Sulawesi and the lawesi for the Tertiary (above). Different timing Philippines may have existed along volcanic arcs, and amounts of rotation are of critical importance such as the long-lived arc along the North Arm of for plate tectonic reconstructions of the region Sulawesi and the Cagayan and Sangihe arcs, and because they would affect the evolution and ac- later along the younger Sulu arc. cretion of material forming eastern Sulawesi and ± The uplift and subsequent erosion of Borneo from the nature of the change between northern main- the late Oligocene to the present day and the land Borneo and the South China Sea. emergence of more extensive land areas in Su- ± The nature, origin and evolution of the Tertiary lawesi led to the progressive reduction in width basins and gulfs in and around Borneo and Su- of the Makassar Straits. This may have facilitated lawesi: notably the Tertiary basins which now 330 M.E.J. Wilson, S.J. Moss / Palaeogeography, Palaeoclimatology, Palaeoecology 145 (1999) 303±337

occur onshore, the Sabah and Sarawak Basins, the whether the North Arm of Sulawesi is ¯oored on Makassar Straits, the Bone, Gorontalo and Tomori ophiolitic, volcanic arc or continental basement. gulfs or bays. Although widespread basin initia- If the basement of the North Arm of Sulawesi tion occurred around the margins of the Sunda- is ophiolitic, can this area be regarded as part of land craton in the Palaeogene, the mechanics and a larger ophiolitic formed in a back-arc setting, reasons for basin formations and detailed basin which might include the Celebes Sea and the East architectures are still unclear. Depositional envi- Sulawesi Ophiolite? ronments varied considerably within and around ± The history of uplift in Sulawesi and Borneo and the margins of these basins, and there is still much how this relates to regional plate tectonic events. work to be undertaken on detailed Tertiary facies Changes in palaeoenvironment through time are variations. very dif®cult to evaluate for regions with no or a ± Further information is required concerning the very thin Cenozoic cover, such as the Sunda Shelf. nature of microcontinental and oceanic fragments Although these areas were probably land areas for and their original af®nities and processes of ac- much of the Cenozoic, sediments deposited dur- cretion onto the eastern margin of the Sundaland ing marine incursions may have been removed by craton. The direction, nature and precise timing later erosion. Further provenance work on clastic of collision=emplacement of the microcontinental sediments and their source lithologies would yield and ophiolitic fragments accreted onto western information on transport routes and distances and Sulawesi in many cases is still unclear. thereby give clues to the timing of formation and ± One of the largest ophiolite complexes in the areal extent of mountain areas. world is located in Sulawesi and the nature, tim- More information on any of the areas discussed ing and origin of this area is of importance both above could then be used to further constrain current in terms of regional plate tectonics and in under- plate tectonic models of the region and re®ne palaeo- standing ophiolite evolution. It is unclear whether geographic interpretations. Additional work on the the ophiolitic sequences in Sulawesi can be re- temporal and spatial distributions of inferred envi- garded as one ophiolite sequence, or as a number ronments or juxtaposition of certain rock types or of accreted ophiolitic slices, possibly of differing structures compared with known economic discov- ages. The area of generation of these ophiolitic eries or present day distributions of biota could aid sequences is still unclear, with origins suggested future exploration or biogeographic studies. Estab- as part of a larger back-arc basin including the lishing a GIS database, including palaeogeographic Celebes Sea, or origination close to a spreading data, plate tectonic information, details of biotic centre in a small back-arc basin. distribution and relationships and economic occur- ± The nature, origin and evolution of the basement rences, capable of being interrogated and displaying lithologies in western Sulawesi and Borneo. Do trends would be an extremely useful tool in future the metamorphic and ultrama®c basement litholo- analysis. gies represent a number of accreted microconti- nental and oceanic fragments, and if so what is the origin and evolution of these different areas? 8. Conclusions Does the nature of the basement lithologies ex- ert a strong control on the subsequent Tertiary The evolution of Borneo and Sulawesi during evolution and sedimentation of the region. the Cenozoic has implications for the plate tectonic ± Further work on the timing, nature and prove- processes involved in the accretion of microconti- nance of the igneous lithologies in western Su- nenal and oceanic material and to the development lawesi and Borneo, particularly the cause of this of volcanic arcs along convergent cratonic margins. magmatism and how igneous activity relates to The maps in this paper are the ®rst attempt to plot plate tectonics. detailed palaeogeographic information onto plate re- ± The nature of the basement in the North Arm of constructions of these islands. Undertaking such a Sulawesi is still highly contentious. It is not clear task helps to highlight discrepancies between plate M.E.J. Wilson, S.J. Moss / Palaeogeography, Palaeoclimatology, Palaeoecology 145 (1999) 303±337 331 tectonic reconstructions and environmental data, and are thanked for their invaluable help and friendship can be used to further constrain plate tectonic models in the ®eld. The constructive comments of the re- and to highlight areas for further study. viewers Charles Hutchison and particularly Theo These islands, as well as being a remarkable nat- van Leeuwen helped to improve the manuscript. ural workshop to study plate tectonic processes, are also of prime importance to biogeographers and ar- eas of proven accumulations and frontier exploration References for natural resources. An increased knowledge of variations in the deposition and=or formation of cer- Achmad, Z., Samuel, L., 1984. Stratigraphy and depositional tain rock types related to plate tectonic changes and cycles in the N.E. Kalimantan Basin. Indones. Pet. Assoc. Proc. Annu. 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