Banda Association Directory UMM :Data Elmu:jurnal:J-a:Journal of Asian Earth Science:Vol18.Issue6.Dec2000:

collided with the Birdshead in the Mid-Tertiary, when the older sediments were folded. More detailed work is needed on the Mesozoic rocks, which are well exposed on the south coast of Misool and the islands immediately to the south, to clarify their role in the regional evolution. 3.6. Australian Margin summary The wide variations in Australian Margin stratigraphies are not surprising in view of the vast area covered. The type area for the association is taken to be the shelf south of Timor the ‘Timor Gap’. Western Irian Jaya, including the Birdshead, and the Sula Spur, are included in this asso- ciation but their basements of Late Paleozoic granites and associated extrusive rocks have more in common with central Papua New Guinea than the Northwest Shelf. Misool island is different again and lacks the terrestrial Triassic ‘red beds’ deposited elsewhere in the region prior to, and at the beginning, of the break-up of this part of Gondwanaland. The later Mesozoic in all areas records a steady increase in water depth, from marginal marine in the Jurassic to open water bathyal in the later Cretaceous. During the Tertiary, parts of the margin were fragmented andor involved in collisions, and Tertiary stratigraphies therefore differ considerably.

4. Banda Association

The Banda Association, which is found on the islands surrounding the Banda Sea, progresses from Upper Triassic to Lower Jurassic shallow water clastics and carbonates which are richly fossiliferous and sometimes bituminous, via unconformity to an Upper Jurassic to Paleogene condensed sequence of deep water carbonates and cherts from which clastic components are almost completely absent. The Middle to Late Jurassic hiatus is an important diagnostic feature. It is widely recognised on the Australian J. Milsom Journal of Asian Earth Sciences 18 2000 761–779 770 La wanopo Fault Undifferentiated Mesozoic Cretaceous limestone Jurassic limestone JurassicTriassic clastics Fig. 7. Distribution of Mesozoic sedimentary rocks in eastern Sulawesi, after Sukamto 1975. J. Milsom Journal of Asian Earth Sciences 18 2000 761 – 779 771 POMPANGEO SCH IST Low to high grade metamorphics Reef Limestone REEF LIMESTONE EAST SULAWESI MELU H U FOR MATION TOKALA FOR MATION CELEBES MOLASSE CELEBES LIMESTONE BURU MATANO FOR MATION WAH LUA COMPLEX RANA COMPLEX DALAN FOR MATION KU MA FOR MATION MEFA FM. Interbedded sandstones, shales, siltstones, some conglomerates Basaltic lavas and tuffs Cherty calcilutites interbedded with conglomerates in the lower part and marl and shale in the upper parts Low grade greenschist facies metamorphosed clastics Marls, calcilutites, conglomerates Conglomerate, sst, lst Coral and foram. lst LEKO FOR MATION FTAU WAEKEN FOR MATION WAKATIN GH EGAN FOR MATION H OTONG Dolomites, shales, some bituminous, limestones Medium-grade greenschist to amphibolite metamorphosed clastics Coral reef Sandstones Coarse to fine grained terrigenous clastics Reefal and nummulitic limestone White to pink porcellaneous pelagic limestones Bituminous limestones, and shales Bathyal fine-grained limestones and argillaceous limestone MIO- CENE OLIGO- CENE PALEO- CENE EOCENE PA L E O Z O IC PLIOCENE EARL Y CRET A CEOUS JURASSIC TRIASSIC PERMIAN MESOZOIC CENOZOIC EARL Y EARL Y MIDDLE LA TE LA TE LA TE M L E MIO- CENE OLIGO- CENE PALEO- CENE EOCENE P AL E OZ OIC PLIOCENE EARL Y CRET A CEOUS JURASSIC TRIASSIC PERMIAN M ESO ZO IC C ENO ZO IC EARL Y EARL Y MIDDLE LA TE LA TE LA TE M L E 100 200 300 100 200 300 8 b 8 a Fig. 8. a Stratigraphic column for East Sulawesi, after Rusmana et al. 1993. b Stratigraphic column for Buru, after Tjokrosapoetro et al. 1993. Numbers in circles refer to locations shown in Fig. 1. Vertical scale in m.y. Northwest Shelf, where it was termed ‘Wombat-type’ by Gradstein 1992 following ODP drilling on the Wombat Plateau. There are many similarities between the Mesozoic sediments of the Wombat Plateau and the Banda Associa- tion. However, whereas the Mesozoic of the plateau rests on a thick unmetamorphosed Paleozoic section, metamorphic rocks, upon which the Triassic sediments are said to rest unconformably, are common in the Banda Association, as are Cretaceous–Paleocene ophiolites. Stratigraphies in the various Banda fragments diverge significantly only after the Oligocene, when many of the blocks were deformed by thrusting. 4.1. Buton Buton is one of the most important islands of the Banda Association because of its present close proximity to Sula- wesi Fig. 1. Drawing in part on work by Fortuin et al. 1990 and De Smet and Hermanto 1991, Davidson 1991 deduced separation from Australia in the Late Trias- sic or Early Jurassic and a transition from pre-rift to syn-rift sedimentation in the Middle to Late Triassic. The Triassic rocks Winto Formation rest on pelitic phyllites and slates Lakansai Formation which are exposed over an area of only about 40 km 2 in the northeast of the island Smith and Silver, 1991. Both the Winto and the overlying Lower Jurassic Ogena Formation consist dominantly of limestone, but the Ogena appears to have been depos- ited in deeper water. Clastic sediments, principally shales, are common in the Winto of southern Buton. Both formations contain abundant organic material that is generally considered to be the source of the island’s asphalt deposits. The poorly exposed later Mesozoic on Buton begins with deep marine siliceous and calcareous mudstones of the Upper Jurassic Rumu Formation and continues with the pelagic limestones with nodules and stringers of red chert of the Tobelo Formation. The Tobelo was originally classi- fied as entirely Upper Cretaceous but has now been shown to extend from the end of Rumu deposition up into the late Eocene or early Oligocene Smith and Silver, 1991. Both the Rumu and the Tobelo were evidently laid down very slowly and their lithologies are consistent with deposition during the drift of an isolated continental fragment. According to Davidson 1991, a hiatus at the top of the Tobelo Formation can be attributed to collision with SE Sulawesi in the Early and Middle Miocene N11. Ophio- lites in southern Buton were probably emplaced at about this time, and compression led to uplift and the establishment of an unconformity representing a hiatus of approximately 3 m.y. The basal sediments of the coarse clastic Tondo Formation, immediately above the unconformity, are mainly carbonate detritus but ultramafic and mafic frag- ments become dominant later, indicating uplift of the ophio- lites above sea level. Tondo Formation deposition was ended by subsidence of Buton to bathyal depths at approximately 5 Ma and the deposition of chalks and marls. Subsequent uplift was accompanied by the development of reefal carbonates. Minor compressional effects can be observed in Upper Pliocene strata, and oblique compression and associated strike-slip faulting may continue to the present day. Quaternary uplift in southern Buton, where spectacular flights of coral terraces rise to almost 500 m above sea level, has been estimated at 2.5 km, but the northern part of the island is now subsiding Davidson, 1991. The history of post-Middle Miocene molasse deposition and ophiolite emplacement on Buton is virtually identi- cal with that of eastern Sulawesi, and the 5 Ma subsi- dence seems much more likely to have been caused by extensional collapse of the entire Sulawesi orogen, of which Buton formed a part Milsom et al., 1999, than by the choking of a subduction zone, as suggested by Davidson 1991. 4.2. Buru The Mesozoic succession on Buru Fig. 8b is virtually identical to that on Buton, even though the two islands are separated by the oceanic North Banda Basin Fig. 1. Bitu- minous Triassic source rocks which are abundantly present in float in rivers in the northwest are directly comparable with the Triassic of Buton, as is most of the Cretaceous section. One distinctive feature of Buru, however, is the presence of some Jurassic igneous material, which may be compared with the rift phase volcanics of the Wallaby Plateau Gradstein, 1992. Buru also differs from Buton in the abundance of metamorphic rocks, which cover almost the whole of the western two-thirds of the island. These metamorphics were divided by Tjokrosapoetro et al. 1993 into the low grade Rana and higher grade Wahlua Complexes. A recent reconnaissance along new roads into the centre of the island confirmed this distinction D. Roques, personal communication, 2000. As on Buton, the depositional environment on Buru became shallower in the Tertiary, but there is no direct evidence for Middle Miocene orogeny. Tjokrosapoetro et al. 1993 described the island as characterised by the absence of thrust faults, imbricated structures, melange or ophiolites. The latest phase of the island’s history has been dominated by very rapid uplift and deposition of thick, coarse alluvial fans Fortuin et al., 1988. However, steep gravity gradients recently mapped in the southeast of the island are difficult to explain except by the presence of concealed, thrust emplaced, ophiolites. 4.3. Seram Buru and western Seram were described by Hamilton 1979 as forming a single microcontinent, and certainly the two islands are stratigraphically very similar. For example, parallels have been drawn between the Rana J. Milsom Journal of Asian Earth Sciences 18 2000 761–779 772 Metamorphics of Buru and the Tehoru Metamorphics of Seram Linthout et al., 1989. The sediments of Seram were divided into allochthonous and para-autochthonous units by Audley-Charles et al. 1979 but this was rendered unconvincing by disagreement amongst the co-authors as to whether the key Nief Beds, which span the time interval from the Jurassic to the Oligocene, were to be assigned to the allochthon or the para-autochthon. A different view based in part on recent exploration drilling has been offered by Kemp and Mogg 1992. In this scheme, the oldest unme- tamorphosed sediments of Seram belong to the Middle to Upper Triassic, clastic-dominated, near-shore Kanikeh Formation, which grades into Lower and Middle Jurassic deep and shallow water limestones Manusela and Saman– Saman Formations, respectively both upwards and later- ally. If these relationships have been correctly interpreted, then all the sediments of Seram can be fitted into a single stratigraphic sequence Fig. 6b. The Kanikeh and Saman–Saman are contemporaneous with, and also strikingly similar to, respectively, the Winto and Ogena Formations of Buton. Only the Manusela Formation appears to lack a direct Buton equivalent. In view of the small area of Mesozoic outcrop on Buton, there may be little significance in this absence, or in the apparently different durations of the Jurassic hiatus. The similarities between Buton and Seram continue above the mid-Jurassic unconformity, since the Late Jurassic Kola Shale of Seram resembles the Rumu Formation of Buton and both are over- lain by deep water condensed sequences dominated by fora- miniferal limestones and marls which extend from the Early Cretaceous into the Paleogene Nief Beds on Seram and Tobelo Formation on Buton. In both the Nief and Tobelo there is evidence for shallower water conditions in the Paleogene and eventual termination of carbonate sedimen- tation in the Miocene. 4.4. Western Kai and the Banda Ridges Silicic schists, gneisses and migmatites on the western- most islands of the Kai group have been correlated by Charl- ton et al. 1991b with the Kobipoto Complex of Seram and were considered by Honthaas et al. 1997 as uplifted parts of a former Banda forearc. Dredging on the high standing ridges Banda Ridges in the central Banda Sea has recovered igneous and meta- morphic rocks Silver et al., 1985, Triassic sediments Villeneuve et al., 1994 and Miocene reefs Corne´e et al., 1998. The metamorphics were originally correlated with those of the Birdshead Silver et al., 1985 but the descrip- tions of the Triassic rocks are much more reminiscent of Buton, Buru and Seram. 4.5. Eastern Sulawesi The geology of eastern Sulawesi is often described in terms of a simple division into belts of schist and ophiolite separated by the Lawanopo Fault Fig. 1, but there are schists to the north of this fault and ophiolites to the south. Patterns of metamorphism are complex. Parkinson 1998 considered that some of the metamorphic rocks formed a high temperature metamorphic sole to the ophio- litic thrusts but it is not clear how widely this interpretation can be applied. Both blueschists and greenschists are present. Metamorphic facies vary and have been used to define a number of distinct formations, but it is possible that these grade into each other. The prevalence of thrusting, and the reconnaissance nature of the mapping in many areas, leave this question open. Gravity data indicate that the ophiolites overlie the schists on a thrust surface with variable but very shallow dip Silver et al., 1978. Relatively small south-block up movement along the Lawanopo Fault could have created the present outcrop pattern by exposing the southern parts of the ophio- lite belt to more intensive erosion. Ultramafics south of the Lawanopo Fault, which might represent deep keels to a previously extensive thrust sheet, are associated with occa- sionally strong but very local positive gravity anomalies. If schists, rather than ophiolites, predominate at depth, then their age and origin are important in any regional synth- esis. The most widely held view is that they represent the basement of a microcontinent which collided with western Sulawesi in the mid-Tertiary Hamilton, 1979. If this is the case, then Australasia seems the most likely ultimate source, although Parkinson 1998 inter- preted the main metamorphic formation, the Pompangeo Schist Complex, as the easternmost extension of the Mesozoic Sundaland Margin, metamorphosed in the Early Cretaceous under intermediate high-pressure conditions. Mesozoic sediments, metamorphosed slightly or not at all, are often ignored in regional descriptions but are very widely distributed in eastern Sulawesi Fig. 7. The main periods represented are the Triassic–Lower Jurassic terres- trial to marginal marine Meluhu Formation and deep water Tokala Formation and Cretaceous deep water carbonate- chert Matano Formation. Kundig 1956 estimated the total Mesozoic section as little more than one kilometre thick on the East Arm, but it may be thicker in the Southeast Arm, where the outcrops are more extensive. He also commented on similarities between the Triassic sedi- ments along the southeastern margin of the East Arm, where they form isolated klippen and comprise bitumi- nous limestones and shales, and those of Buru. Surono 1998, in describing the Meluhu Formation, noted that palaeomagnetic determinations placed the site of deposi- tion close to the then latitude of the North Australian Margin. The Cretaceous deep water sediments are generally spatially associated with the ophiolite and might be supposed to constitute its uppermost part. However, Parkinson 1998 cited age relationships and the reported existence of depositional contacts between the Matano Formation and the schists as arguments against J. Milsom Journal of Asian Earth Sciences 18 2000 761–779 773 J. Milsom Journal of Asian Earth Sciences 18 2000 761 – 779 774 MIO- CENE OLIGO- CENE PALEO- CENE EOCENE PA L E O Z O IC PLIOCENE EARL Y CRET A CEOUS JURASSIC TRIASSIC PERMIAN MESOZOIC CENOZOIC EARL Y EARL Y MIDDLE LA TE LA TE LA TE M L E h i a t u s ? h i a t u s ? erosional hiatus Claystone and shale with interbedded limestones, calcilutites and siltstones Interbedded calcilutites and thin shales with radiolaria, foraminifera and chert nodules Massive to thickly bedded calcarenites, calcirudites and recrystallised limestones ATAH OC FOR MATION OFU FOR MATION VIQU EQU E GR OU P BOBO- NAR O TIMOR PARA- AUTOCHTHON TIMOR ALLOCHTHON MAU BISSE FOR MATION AITU TU LIMESTONE BABU LU FOR MATION NIOF FOR MATION WAI LU LI FOR MATION OE BAAT FOR MATION NAKFU NU FOR MATION MENU FOR MATION MIO- CENE OLIGO- CENE PALEO- CENE EOCENE PLIOCENE Limestone and radiolarian chert with volcanics and tuffaceous clastics Volcanics and tuffaceous clastics Agglomerate and tuff Basalts and tuffs Shallow marine bioclastic limestone EARL Y CRET A CEOUS ME SO ZOI C C EN OZO IC LA TE LA TE METAN FOR MATION OCU SSI VOLCANICS CABLAC LIMESTONE H AU LASI FOR MATION NONI FOR MATION MU TISLOLOTOI COMPLEX Radiolaria-rich limestones and shales Silts, shales and sandstones Red crinoidal limestones and basaltic pillow lavas Shales with minor sandstones and tuffs. Weakly metamorphosed at base. Slates, phyllites, meta- quartzites, schists, rare marble. Shales with thin fine grained sandstones turbidites Varied deep and shallow water deposits Scaly clay Interbedded calcilutites and thin shales with radiolaria, foraminifera and chert nodules Massive glauconitic sandstone Medium-grade metamorphics and ophiolite AILEU FOR MATION K O L B ANO S E Q U E NC E KE KN E N O S E Q U E N C E 100 100 200 300 9 a 9 b Fig. 9. a Stratigraphic column for the Timor parautochthon and autochthon, after Sawyer et al. 1993 and Reed et al. 1996. b Stratigraphic column for the Timor allochthon, after Sawyer et al. 1993 and Earle 1983. Numbers in triangles refer to locations shown in Fig. 1. Vertical scale in m.y. this assumption. The stratigraphic column for East Sula- wesi shown in Fig. 8a is compared with the column for Buru, where the proportions of outcrop of metamorphic rocks and sediments are similar, although ophiolites are absent. 4.6. Banda Association summary The Banda Association is characterised by a variety of metamorphic rocks, some of which may represent continen- tal basement and others which may be the metamorphic soles to ophiolite sheets, and ophiolitic rocks which are only occasionally strongly metamorphosed. The sedimen- tary record begins in the Triassic with deposition under fluvial or marginal marine conditions. Water depths increased, and carbonate deposition became more wide- spread, in the Early Jurassic. Sediments of this generally conformable sequence are frequently bituminous. They are found in outcrop on Buton where they source asphalt deposits; Davidson, 1991 and Buru, and source oil on Seram Peters et al., 1999. A characteristic feature of the Banda Association is the presence of a major unconformity encompassing at least a major part of the Late Jurassic and sometimes much of the Middle Jurassic and Early Cretaceous. The sediments immediately above this unconformity are generally shales but quickly give way to condensed sequences of carbonates with cherts, deposited in environments remote from sources of clastic sedimentation. This type of sedimentation contin- ued into the Paleogene, when a second major unconformity developed, interpreted here as a consequence of collision between a microcontinent and the margin of Sundaland. The subsequent history of the association can be interpreted in terms of post-orogenic collapse and dispersal, with early molasse deposition and, in some cases, later collision with the advancing Australian Margin around the Banda Arc.

5. Timor