Provenance of Mesozoic Sandstones in the Banda Arc Indonesia

IPA14-G-301

PROCEEDINGS, INDONESIAN PETROLEUM ASSOCIATION Thirty-Eighth Annual Convention & Exhibition, May 2014

PROVENANCE OF MESOZOIC SANDSTONES IN THE BANDA ARC, INDONESIA

Sebastian Zimmermann* Robert Hall*

ABSTRACT in rocks from Sumba suggest that they are mainly derived from metamorphic sources. Mesozoic to Quartz-rich sandstones in the outer Banda Arc Archean zircons from Sumba suggest derivation Islands are the equivalent of Mesozoic sandstones from Australian crust that had collided in Sulawesi along the northern Australian margin and are during the Cretaceous. important potential hydrocarbon reservoirs. They have been exposed by on-going collision of INTRODUCTION Australia and Asia, resulting in the opportunity to study their provenance. Previous studies suggest The Banda Arc is situated in eastern Indonesia that rivers draining Australia will have provided between Australia, New Guinea and Sulawesi most sedimentary input. There have been (Figure 1). In the outer arc islands of Seram, suggestions of a northern provenance for some Tanimbar, Babar, Timor and Sumba there are Timor sediments. Mesozoic sandstones which have been exposed as a result of on-going convergence and subduction Conventional light mineral plots of sandstones from processes. Many of the exposed rocks are the the samples of the various Banda Arc islands equivalents of the formations offshore that include typically show recycled orogen and/or continental important hydrocarbon reservoirs. block as origin, consistent with an Australian source. However, many of the sandstones are A number of palaeogeographic models have been texturally immature. Many samples also contain proposed for the region (e.g. Metcalfe, 2011; volcanic quartz and volcanic lithic fragments. Charlton, 2012; Hall, 2012). However detailed Heavy mineral assemblages dominated by rounded detrital sediment pathways are unknown for the ultra-stable minerals are typical for most samples. Banda Arc and the main sediment sources and However these are commonly mixed with angular dynamic variations in sediment provenance over grains. Most samples predominantly contain heavy time need to be identified. It is widely assumed that minerals from acidic igneous and metamorphic many of the quartz-rich sandstones have an rocks. A few samples contain grains from mafic or Australian origin. New information is required for a ultramafic origin. Detrital zircon (LA-ICP-MS) U- larger regional interpretation and assessment of Pb ages range from Archean to Mesozoic, but existing models. variations in age populations indicate differences in source areas along the Banda Arc in locality and This paper discusses the provenance of a number of time. siliciclastic formations, in particular Triassic, Jurassic and Cretaceous sandstones from the islands In the Tanimbar Islands and Babar, sediment came of Tanimbar, Babar, Timor and Sumba (Figure 1). from both Australian basement and acidic igneous Interpretations are based on light and heavy mineral rocks from the Bird’s Head. Sandstones in Timor analysis, as well as on U-Pb ages of detrital zircons. show a difference in provenance from east to west. The data presented here represent the first The east contains a greater acidic igneous signature, systematic regional study of heavy minerals and whereas the west is more dominated by detrital zircon ages from the large area of the Banda metamorphic sources in the Triassic and suggests Arc. Results from this study are compared to those better connectivity to continental Australia from the from earlier studies in the area (Cook, 1987; Bird, Jurassic to Cretaceous. Cretaceous zircon ages, 1987; Bird and Cook, 1991; Hasan, 1992; Barber et heavy minerals and immature textures al., 2003; Smyth et al., 2007; Sevastjanova et al., 2011; Southgate, 2011). * Royal Holloway, University of London

GEOLOGICAL BACKGROUND 206Pb/U238 age 337.13 +/- 0.37 Ma (Slama et al., 2008) and NIST 612 silicate glass (Pearce et al., Audley-Charles (1965) postulated the outer Banda 1997) were used as external standards for correcting Arc islands were located well within the mass fractionation and instrumental bias. Zircon northwestern Australian margin throughout the ages with discordance higher than 10% were whole Mesozoic. It is thought that they were close filtered and excluded. to the Quiantang and Sibumasu blocks to the north until the Early Permian, the Lhasa and Woyla Thin sections were prepared at Royal Holloway blocks until the Late Triassic (Metcalfe, 1996), and University of London and partly stained for feldspar the Argo and Banda Blocks until the Late Jurassic identification. Optical light microscopy was (Hall, 2012). The initial drift of the Banda block in conducted to identify minerals, and assess internal the Late Jurassic formed the Banda embayment and textures such as sorting and rounding (Figure 3A) left the Sula Spur northeast of Australia (Klompé, and the presence of volcanic quartz and lithic 1954). The embayment was surrounded by a passive volcanic fragments (Figure 3B). Rocks were continental margin (Hall, 2011) and from the Late classified after Folk (1968). Sandstone provenance Jurassic the present-day areas of Timor, Tanimbar, was determined from detrital modes, heavy mineral Seram and Southeast Sulawesi were within this analysis and U-Pb geochronology of detrital margin (Audley-Charles, 1965). The crust in the zircons. Modal counts were used in standardised outer Banda Arc islands is composed of fragments Gazzi-Dickinson diagrams (Dickinson et al., 1983; originating mostly from the NW Australian margin Ingersoll et al., 1984) giving statistical (southern outer arc islands and northern Sula Spur) compositional comparisons and information about and fragments that formed part of the Sunda Arc source rock data (Figure 2). Heavy mineral data and the Asian margin (including young oceanic were obtained by using slides with heavy mineral crust) by the Late Mesozoic (Hall, 2002). separates embedded in Canada Balsam/turpentine Palaeogeographic reconstructions by Metcalfe (refractive index n= 1.55). The transparent heavy (Metcalfe, 2011) and Hall (Hall, 2012) imply that minerals were point counted for statistical Sumba was part of the northern Australian margin evaluation (Morton and Hallsworth, 1994; Mange- from at least the Early Permian until the Late Rajetzky, 1995). The heavy mineral distributions Jurassic, collided with the Asian margin in the Late within the Banda Arc islands sandstones are Cretaceous, and moved south to its present day displayed in Figure 4. Zircon (Figure 3C) and position in the Miocene. Barber et al. (2003) tourmaline morphologies were analysed to aid suggested that the source of much of the sediment evaluation of transport history. The common ultra- input to the outer Banda Arc islands were rivers stable heavy minerals were grouped by their most draining northern Australia. Palaeocurrent data have likely protoliths into acidic igneous, basic igneous been interpreted to suggest that some parts of Timor and metamorphic origin (Figure 3D and Figure 4). also received sediment input from a northern source The detrital zircon U-Pb ages of selected samples (Cook, 1983; Bird, 1985). were compared to each other and prospective source areas that could have supplied detritus (by volcanic METHODOLOGY activity and erosion). To visualise similarities and possible source areas, some results are plotted on Sandstone samples underwent routine mineral probability plots and histograms, and kernel density separation at the Southeast Asia Research Group plots (Bishop, 1999) in Figure 5. The results sediment laboratory, located at Royal Holloway obtained from different areas are discussed below. University of London. To conduct heavy mineral analysis and detrital zircon U-Pb dating, samples TANIMBAR ISLANDS were crushed, washed, sieved and separated (using The small islands to the west of Yamdena are heavy liquid and magnetic separation methods). characterised by Mesozoic sandstones, siltstones Zircons were handpicked and mounted for U-Pb and mudstones. In general, the sandstones are laser ablation inductively coupled plasma mass exposed in massive cliffs and locally contain well- spectrometer (LA-ICP-MS) dating. Single grains bedded successions. They are bright beige to grey were dated at University College London with a coloured and fine to coarse grained. New Wave 213nm aperture imaged frequency- quintupled laser ablation system (35-25nm) coupled Triassic Maru Formation to an Agilent 7500 quadrupole-based ICP-MS. The Glitter data reduction software was used to process Triassic sediments in the Tanimbar Islands are the LA-ICPMS data acquired. Plesovice zircon predominantly shallow marine sand and siltstones

(sublithic arenites, lithic wackes). Typical Triassic (Samples TAN 18, TAN 36) range from Jurassic to outcrops contain well-bedded sandstones with Archean; the youngest grain is Lower Jurassic interbedded siltstones. Locally, herring-bone cross (195.7 Ma - TAN 36), and the oldest grain is stratification and hummocky structures are common Archean (3.2 Ga – TAN 36). Characteristic peaks as well as gradational coarsening upwards. occur in the Permo-Triassic and at 1.8 Ga, with minor peaks in the Neoproterozoic and at 1.2 Ga Textures show poor to moderate sorting and sub- (Figure 5). The average age distribution is 4% angular to rounded grains. Detrital modes (Figure 2) Archean, 53% Proterozoic and 43% Phanerozoic. suggest a recycled orogen origin. Some volcanic input is indicated by an average of 15% volcanic Cretaceous Ungar Formation quartz (max. 21%) and 13% volcanic lithic fragments (max. 18%). Heavy minerals (samples Lower Cretaceous rocks of the upper Ungar TAN 25, TAN 23, TAN 13, TAN 26, TAN 24 and Formation are massive white-beige to yellowish TAN 35) consist on average of grains which are fine- to coarse-grained sandstones (quartz arenite, 65% acidic igneous/hydrothermal, 21% subfeldspathic arenite, arkosic arenite). Thin metamorphic, 10% basic igneous and up to 4% parallel lamination and medium-scale cross-bedding ultramafic affiliation (Figure 4). Average are common. morphologies of zircons and tourmaline are dominated by idioblastic grains (zircons: 57% Textures show poor to well sorted character and idioblastic vs 43% rounded, tourmaline: 60% sub-rounded to rounded grains. Detrital modes idioblastic vs 31% rounded). Zircon U-Pb ages suggest a recycled orogen to continental block (Samples TAN 9, TAN 13, TAN 24) range from origin (Figure 2). Additional volcanic input is given Triassic to Archean; the youngest grain is Upper by an average of 15% volcanic quartz (max. 34%) Triassic (203.1 Ma - TAN 9), and the oldest grain is and 8% volcanic lithic fragments (max. 12%). Archean (3.4 Ga – TAN 13). Characteristic peaks Heavy minerals (samples TAN 10, TAN 11, TAN, occur in the Permo-Triassic/ Carboniferous and 1.8 19, TAN, 20, TAN 28, TAN 30 and TAN 45) Ga. The average age distribution is 2% Archean, consist on average of 72% acidic 34% Proterozoic and 64% Phanerozoic (Figure 5). igneous/hydrothermal, 23 % metamorphic and max. The spectrum shows similarities with the Bird’s 2% basic igneous to ultramafic (max. 3%) Head Tipuma Formation (Ig10-PR31 in Gunawan, affiliation (Figure 4). Average morphologies of 2011). zircons and tourmaline are dominated by rounded grains (zircons: 48% idioblastic vs 52% rounded, Jurassic Ungar Formation tourmaline: 39% idioblastic vs 61% rounded). Zircon U-Pb ages (Samples TAN 11, TAN 28, TAN Jurassic rocks in the Tanimbar Islands are typically 45) range from Cretaceous to Archean; the youngest massive sandstones of the Ungar Formation and are grain is Cretaceous (83.7 Ma - TAN 28), and the widespread, especially in the islands between Selu oldest grain is Archean (3.2 Ga – TAN 28). and Maru. They comprise immature massive Characteristic peaks occur in the Cretaceous, greyish brown sandstones (quartz arenite, sublithic Permian and the Cambrian/Neoproterozoic arenite, subfeldspathic arenite) with fine to medium (Figure 5). The average age distribution is 3% grain size. Archean, 45% Proterozoic and 52% Phanerozoic.

Textures show poor to well sorted character and BABAR sub-angular to rounded grains. Detrital modes suggest recycled orogen (Figure 2). Additional Triassic Maru/ Tela Formation volcanic input is shown by an average of 15% Triassic rocks in Babar are exposed to the east of volcanic quartz (max. 30%) and 10% volcanic lithic the central mud volcano along several ridges that fragments (max. 18%). Heavy minerals (samples stretch northeast-southwest. They consist of grey- TAN 6, TAN 9, TAN 18, TAN 31, TAN 36) consist green fine-grained sandstones (sublithic arenite, on average of 68% acidic igneous/hydrothermal, 24 lithic arenite) with distinctive mud clasts and plant % metamorphic and max. 7% basic igneous to fragments. ultramafic (max. 1%) affiliation (Figure 4). Morphologies of zircons and tourmaline are Textures show moderate to very well sorted dominated by idioblastic grains (zircons: 58% character and sub-angular to sub-rounded grains. idioblastic vs 42% rounded, tourmaline: 67% Detrital modes (Figure 2) suggest a recycled orogen idioblastic vs 33% rounded). Zircon U-Pb ages to continental block origin. Additional volcanic

input is given by an average of 12% volcanic quartz biostratigraphic indicator. Outcrops in East Timor (max. 18%) and 16% volcanic lithic fragments are found in in the Cribas anticline and in the east (max. 22%). Heavy minerals (samples BAB 5, BAB close to the village of Com. 13, BAB 22 and BAB 23) consist on average of 66% acidic igneous/hydrothermal, 21 % Textures show well to very well sorting and angular metamorphic and max. 10% basic igneous to to sub-angular grains. Detrital modes (Figure 2) ultramafic (max. 3%) affiliation (Figure 4). Average suggest recycled orogen to magmatic arc origin. morphologies of zircons and tourmaline are Additional volcanic input is given by an average of dominated by idioblastic grains (zircons: 60% 13% volcanic quartz (max. 26%) and, 19% volcanic idioblastic vs 40% rounded, tourmaline: 69% lithic fragments (max. 30%). Heavy minerals idioblastic vs 31% rounded). Zircon U-Pb ages (samples ET 4, ET 5, ET 13 and ET 16) consist on (Samples BAB 5, BAB 13) range from Triassic to average of 44% acidic igneous/hydrothermal, 37% Archean; the youngest grain with is Triassic (209.5 metamorphic, 9% basic igneous to max. 10% Ma – BAB 5), and the oldest grain is Archean (2.6 ultramafic affiliation (Figure 4). Average Ga – BAB 5). Characteristic peaks occur in the morphologies of zircons are dominated by rounded Permo-Triassic/, Devonian and at 1.8 Ga (Figure 5). grains (zircons: 48% idioblastic vs 52% rounded), The average age distribution is 57% Proterozoic and the average of tourmaline by idioblastic grains 43% Phanerozoic. The spectrum shows strong (71% idioblastic vs 29% rounded). Acquisition of similarities to the Triassic Maru Formation in zircon U-Pb ages is in progress. Tanimbar. Triassic Babulu Formation Jurassic Sandstone Unit The few outcrops along the northern coast of East Jurassic outcrops are limited to the northern edge of Timor are Triassic sandstones (lithic arenite), which the central basin beside the river. Sandstones are commonly similar to the Babulu Formation in (arkosic wacke) are of light grey colour and West Timor. Fine- to medium grained grey commonly contain plant fragments. sandstones are intercalated with decimetre thick mudstone layers. Textures show moderate to well sorted character and sub-angular grains. Detrital modes (Figure 2) Textures show moderate to well sorted character suggest recycled orogen origin. Additional volcanic and sub-angular grains. Detrital modes (Figure 2) input is given by up to 20% volcanic quartz and suggest a recycled orogen origin. Additional 14% volcanic lithic fragments. Heavy minerals volcanic input is given by 1% volcanic quartz and (samples BAB 34, BAB 35) consist on average of 24% volcanic lithic fragments. Heavy minerals 37% acidic igneous/hydrothermal, 41 % (summarised samples ET 9, ET 11) consist in metamorphic and max. 22% basic igneous average of 33% acidic igneous/hydrothermal, 40% affiliation (Figure 4). Average morphologies of metamorphic, 5% basic igneous to 22% ultramafic zircons and tourmaline are slightly dominated by affiliation (Figure 4). Average morphologies of rounded grains (zircons: 51% idioblastic vs 49% zircons and tourmaline are dominated by idioblastic rounded, tourmaline: 68% idioblastic vs 32% grains (zircons: 83% idioblastic vs 17% rounded, rounded). Zircon U-Pb ages (Sample BAB 35) tourmaline: 77% idioblastic vs 23% rounded). range from Jurassic to Archean; the youngest grain Acquisition of zircon U-Pb ages is in progress. is Lower Jurassic (193.4 Ma), and the oldest grain is Palaeoproterozoic (2.1 Ga) (Figure 5). Cretaceous Seical Formation Characteristic peaks occur in the Permo-Triassic, Devonian and at 1.8 Ga. The average age To the east of Beaucau a small ridge exposes distribution is 1% Archean, 36% Proterozoic and lithologies of the Cretaceous Seical Formation. 63% Phanerozoic. Grey-green to reddish sandstones (arkosic wacke) are evenly bedded and strongly weathered. They are EAST TIMOR finely laminated and locally contain cross-bedding structures. Permian Atahoc and Cribas Formations Textures show a well sorted character and angular The Atahoc and Cribas Formations contain to sub-angular grains. Detrital modes (Figure 2) laminated sandstones and shales (lithic wacke, lithic suggest a recycled orogen origin. Additional arenite). Atomodesma sp. is a common volcanic input is given by an average of 18%

volcanic quartz and up to 7% volcanic lithic Textures show poor to well sorted character and fragments. Heavy minerals (ET 17) consist of 59% angular to sub-angular to sub-rounded grains. acidic igneous/hydrothermal, 40% metamorphic, Detrital modes (Figure 2) suggest a recycled orogen 1% basic igneous to max. 10% ultramafic affiliation origin. Additional volcanic input is given by an (Figure 4). Average morphologies of zircons are average of 14% volcanic quartz and 16% volcanic dominated by rounded grains (35% idioblastic vs lithic fragments. Heavy minerals (samples SZ 47 65% rounded), shapes of tourmaline by idioblastic and SZ 49) consist on average of 55% acidic (74% idioblastic vs 26% rounded). Zircon U-Pb igneous/hydrothermal, 38% metamorphic, 1% basic ages (Sample ET 17) range from Cretaceous to igneous to max. 6% ultramafic affiliation (Figure Archean; the youngest grain is Cretaceous 4). Average morphologies of zircons and tourmaline (97.3 Ma), and the oldest grain is Archean (2.6 Ga). are dominated by idioblastic grains (zircons: 54% Characteristic peaks occur in the Cretaceous, idioblastic vs 46% rounded, tourmaline: 79% Jurassic, Permian and Cambrian/Neoproterozoic idioblastic vs 21% rounded). Zircon U-Pb ages (Figure 5). The average age distribution is 1% (Samples SZ 37, SZ 49) range from Jurassic to Archean, 40% Proterozoic and 59% Phanerozoic. Archean; the youngest grain is Lower Jurassic (209.5 Ma – SZ 49), and the oldest grain is Archean WEST TIMOR (2.9 Ga – SZ 49). Characteristic peaks occur in the Permian and at 1.8 Ga (Figure 5). The average age Triassic Niof Formation distribution is 1% Archean, 63% Proterozoic and 36% Phanerozoic. Triassic siliciclastic sediments in West Timor were collected in the Kekneno area. The Niof Formation SUMBA consists of fine-grained dominantly shaly rocks with minor siltstones and sandstones (lithic wacke, lithic Cretaceous Lasipu Formation arenite). A bivalve fauna of Daonella and Halobia (de Roever, 1940) is common in some layers and The Lasipu Formation in Sumba varies locally with indicates the Triassic age. considerable internal variations. In central Sumba, the northern part of the formation consists of Textures show moderate to well sorted character massive grey-bluish siltstones/ meta-pelites (lithic and sub-angular grains. Detrital modes (Figure 2) arenite) that are very hard and dense. In the suggest a recycled orogen to magmatic arc origin. southwest of the island there are decimetre thick, Additional volcanic input is given by an average of well bedded siltstones, and in the south there are 20% volcanic quartz and 8% volcanic lithic turbiditic siltstones with sandstone interlayers fragments. Heavy minerals (samples SZ 17, SZ 18 (sublithic arenite). and SZ 48) consist on average of 30% acidic igneous/hydrothermal, 41% metamorphic, 2% basic Textures of the Lasipu Formation are moderately to igneous to 27% ultramafic affiliation (Figure 4). very well sorted, while the grain shapes are Average morphologies of zircons and tourmaline commonly angular to sub-rounded. Detrital modes are dominated by idioblastic grains (zircons: 68% (Figure 2) suggest recycled orogen to magmatic arc idioblastic vs 32% rounded, tourmaline: 69% (dissected and transitional) origin. Volcanic input is idioblastic vs 31% rounded). Zircon U-Pb ages given by an average of 10% volcanic quartz (max. (Samples SZ 17, SZ 48) range from Triassic to 19%) and 28% volcanic lithic fragments (max. Archean; the youngest grain is Triassic (237.2 Ma – 34%). Heavy minerals are dominated by SZ 17), the oldest grain is Archean (2.7 Ga – SZ metamorphic (75%) origin, ultramafic to basic 48). Characteristic peaks occur in the Permo- igneous (6%) and acidic igneous (19%) (Figure 4). Triassic, Carboniferous and at 1.8 Ga (Figure 5). Average morphologies of zircons and tourmaline The average age distribution is 5% Archean, 45% are dominated by idioblastic grains (zircons: 65% Proterozoic and 50% Phanerozoic. idioblastic vs 35% rounded, tourmaline: 73% idioblastic vs 27% rounded). Zircon U-Pb ages Jurassic Oe Baat Formation (samples SUM 24, SUM 30) range from Cretaceous to Archean; the youngest grain is Upper Cretaceous In the south of West Timor there are large Jurassic (64.1 Ma – SUM 24), and the oldest grain is outcrops in the Kolbano area that form distinct high Archean (2.8 Ga – SUM 24). Characteristic peaks relief ridges. The upper belemnite-bearing occur in the Cretaceous, Triassic, sandstone (arkosic wacke) is part of the Jurassic Cambrian/Neoproterozoic and at 0.9 Ga, with a succession and assigned to the Oe Baat Formation. minor peak at 1.8 Ga (SUM 24) (Figure 5). The

average age distribution is 5% Archean, 57% and East Timor contain zircons that indicate Proterozoic and 38% Phanerozoic. reworking of Triassic and Jurassic formations, plus additional Cretaceous and also Jurassic populations DISCUSSION that suggest an Asian rather than Australian origin (Figure 5). These sandstones are from the upper Conventional light mineral plots of sandstones nappes of Tanimbar (The Western Isles province of (Figure 2) from the Banda Arc islands typically Charlton et al., 1991) and the Banda allochthon indicate a recycled orogen and/or continental block (Audley-Charles, 2011) on Timor which represent origin, consistent with an Australian source. overthrust Asian margin rocks. However, many of the sandstones are texturally immature with sub-angular to angular grain shapes. CONCLUSIONS Many samples also contain volcanic quartz and volcanic lithic fragments derived from a source Islands of the Banda Arc were part of the Australian other than the Australian continent, possibly margin during the Late Palaeozoic and much of the transported and contributed as ash cloud deposits. Mesozoic. It has been generally assumed that Heavy mineral assemblages dominated by rounded quartz-rich sandstones of the Banda Arc were ultra-stable minerals are typical of most samples. derived entirely from Australian sources and However these are commonly mixed with angular sediment was carried north by large rivers draining idioblastic grains. The heavy mineral content of the Australian continent. It is therefore surprising to most samples is composed predominantly of find that many of the Triassic and Jurassic material from acidic igneous and metamorphic sandstones are texturally immature and have zircon rocks. A few samples contain grains with a mafic or ages that suggest that they were derived from the ultramafic origin. Detrital zircon (LA-ICP-MS) U- Bird’s Head, although there are clear contributions, Pb ages range from Archean to Mesozoic, but marked by increased abundances of Precambrian variations in age populations indicate differences in zircons, of input from Australia. In the Triassic the source areas along the Banda Arc in locality and Bird’s Head was part of the palaeo-Pacific active time. margin and quartz and zircons could have been deposited from air-fall deposits or by rivers draining Triassic rocks from Tanimbar, Babar and West the hinterland behind the arc. Timor have abundant Permo-Triassic zircon populations (Figure 5). We interpret these as Cretaceous sandstones from Sumba, East Timor and indicating a Bird’s Head provenance based on Tanimbar all contain zircons that suggest reworking comparison of zircon ages and textures with the of older Triassic and Jurassic sediments, but also Tipuma Formation of West Papua (Gunawan, 2013; Jurassic and Cretaceous zircon populations that Gunawan et al., 2012; 2014). The Triassic Bird’s indicate igneous sources. We suggest these Head sandstones have a significant volcanic quartz represent fragments rifted from the Australian component and this accounts for the texturally margin that separated in the Late Jurassic and were immature character of the sandstones from added to SE Asia in the Late Cretaceous which Tanimbar, Babar and West Timor. record volcanic activity associated with rifting and accretion to the active Sundaland margin. The Jurassic rocks of Babar appear similar to the Triassic, suggesting local reworking processes. In ACKNOWLEDGMENTS contrast, Tanimbar and West Timor Jurassic sandstones contain detrital zircon populations of This project is funded by the SE Asia Research Meso – and Neo- Proterozoic ages (Figure 5) which Group Consortium. We thank Afif Saputra and Inga we suggest are probably derived from northern Sevastjanova for assistance and help in the field. Australia. Thanks also to Dr Andy Beard, Prof Andrew Carter, Dr Martin Rittner, Dr Pieter Vermeesch (UCL) and Cretaceous sandstones from Sumba have distinctive Dr Anna Bird (RHUL) for help and support metamorphic heavy mineral assemblages that acquiring geochronological data and evaluating resemble Sulawesi sandstones (Hasan, 1992) and heavy mineral analysis. zircon age populations support this source. Mesozoic to Archean zircons (Figure 5) suggest REFERENCES derivation from Australian crust that had collided in Sulawesi during the Cretaceous and was available Audley-Charles, M.G., 1965. Permian for erosion. Cretaceous sandstones from Tanimbar palaeogeography of the northern Australia-Timor

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Figure 1 – Regional overview of the Banda Arc Islands Sumba, Timor, Babar and Tanimbar, showing stratigraphic affiliation (Fm = Formation) and rock types collected, classified after Folk (1968). The formations that were analysed and are discussed in this paper are shown.

Figure 2 – Ternary diagrams showing detrital modes of sandstones in the Banda Arc, indicating textures (sorting and rounding) and the tectonic setting according to Dickinson & Suczek (1979). Q – quartz, F – feldspar, L – lithic volcanic fragments

Figure 3 – A) Classification of textures (sorting and rounding) in this study with examples from sandstones in the Banda Arc. B) Examples of volcanic quartz and volcanic lithic fragments. C) Examples of zircon morphologies appearing in samples analysed (left to right – rounded, sub-rounded, elongate- euhedral, elongate-subrounded, euhedral, matrix attached). D) Table for source rock association of heavy minerals appearing in samples analysed for the Banda Arc sandstones (Zrn=Zircon, Tur=Tourmaline, Ap=Apatite, An=Anatase, Mnz=Monazite, Xe=Xenotime, Sph=Sphalerite, Ba=Baryte, Rt=Rutile, Grt=Garnet, Al-sili=Al-silicates (Andalusite, Sillimanite), Cor=Corundum, Ep=Epidote, ClZo=Clinozoisite, Zo=Zoisite, Ves=Vesuvianite, Amph=Amphibole, Pr=Prehnite, St=Staurolite, Dol=Dolomite, All=Allanite, Ttn=Titanite, OPX=Orthopyroxene, CPX= Clinopyroxene, Cr-Sp=Chrome spinel). Apatite and amphibole (circled) are not assigned to any source rocks due to their common occurrence in different rock types.

Figure 4 – Heavy mineral compositions in the Banda Arc, grouped by source rock character based on the affiliations shown in Figure 3. The small pie diagrams indicate morphologies of zircon (grey) and tourmaline (brown): idioblastic-euhedral, subhedral, elongated, matrix-attached, rounded-sub-rounded, rounded.

Figure 5 – Zircon U-Pb age histograms showing the numbers of grains for different ages (bin widths are 10 Ma for Phanerozoic and 50 Ma for Precambrian). Formations from the islands of Tanimbar, Babar, Timor and Sumba are grouped by their depositional age. The Kernel density estimate plot (bottom right) shows the direct comparison between each formation and highlights (red boxes) similarities between the different areas and allows interpretations about provenance.