Geology and mineral resources of the Northern Territory Ahmad M and Munson TJ (compilers) Northern Territory Geological Survey Special Publication 5 Chapter 35: Arafura Basin BIBLIOGRAPHIC REFERENCE: Ahmad M and Munson TJ, 2013. Chapter 35: Arafura Basin: in Ahmad M and Munson TJ (compilers). ‘Geology and mineral resources of the Northern Territory’. Northern Territory Geological Survey, Special Publication 5. Disclaimer While all care has been taken to ensure that information contained in this publication is true and correct at the time of publication, changes in circumstances after the time of publication may impact on the accuracy of its information. The Northern Territory of Australia gives no warranty or assurance, and makes no representation as to the accuracy of any information or advice contained in this publication, or that it is suitable for your intended use. You should not rely upon information in this publication for the purpose of making any serious business or investment decisions without obtaining independent and/or professional advice in relation to your particular situation. The Northern Territory of Australia disclaims any liability or responsibility or duty of care towards any person for loss or damage caused by any use of, or reliance on the information contained in this publication. Arafura Basin Current as of September 2012 Chapter 35: ARAFURA BASIN M Ahmad and TJ Munson INTRODUCTION Creek Orogen. To the west, it is unconformably overlain by relatively undeformed Mesozoic and Cenozoic sedimentary The Neoproterozoic to Permian Arafura Basin extends rocks of the Money Shoal Basin, which are up to 4.5 km from the onshore Northern Territory into Indonesian waters thick (Figure 35.2). This succession is continuous with that (Figure 35.1) and covers an area of about 500 000 km2. of the Bonaparte Basin to the west, but thins rapidly to the Structurally, the basin consists of northern and southern east, so as to form the onlapping edge of a vast Mesozoic sections separated by the large deformed Goulburn Graben to Cenozoic depositional area that extends over much of (Bradshaw et al 1990; equivalent to Arafura Graben of offshore northwestern Australia (Bradshaw et al 1990, Petroconsultants 1989). The Goulburn Graben is a west- Struckmeyer 2006b). Mesozoic and Cenozoic sedimentary northwest-trending asymmetric feature, over 350 km long rocks of the Carpentaria Basin onlap the Arafura Basin and up to 70 km wide, that contains a sedimentary section to the east and southeast, and are up to 1760 m thick. The in excess of 10 km thick. The region to the north of the northern limits of the Arafura Basin are not well de¿ned, Goulburn Graben forms the basin’s main depocentre and although seismic data indicate that it extends towards contains a sedimentary succession up to 15 km thick the Aru Ridge and Merauke Rise to the south of Papua, (Figures 35.2, 35.3). South of the Goulburn Graben a north- Indonesia (Moss 2001). Palaeozoic sedimentary rocks are dipping relatively undeformed ramp that extends onshore also known from central Papua, indicating that the original contains up to 3 km of sedimentary rocks. The Arafura limits of the basin prior to Mesozoic tectonism may have Basin succession comprises sandstone, shale, limestone, been at least this far to the north (Fortey and Cocks 1986, dolostone, coal beds and glacial deposits and is summarised Nicoll and Bladon 1991). To the northwest, the poorly in Figure 35.4 and Table 35.1. Totterdell (2006) described explored Barakan Basin in Indonesian waters is of similar four main phases of deposition within the basin (Basin age and has a similar structure to that of the Arafura Basin phases 1–4) in the Neoproterozoic (Wessel Group), middle (Barber et al 2004). Cambrian–Early Ordovician (Goulburn Group), Late This chapter focuses on the onshore sedimentary Devonian (Arafura Group) and Late Carboniferous–Early succession of the Arafura Basin in the NT. A full discussion Permian (Kulshill Group equivalent). These basin phases of the other components of the basin is beyond the scope were separated by long, relatively tectonically quiescent of this volume, although brief summaries of the offshore periods of non-deposition and erosion. Neoproterozoic and successions are also included. Signi¿cant studies of the Cambrian sedimentary rocks, which outcrop on the northern Arafura Basin and in particular, the onshore succession, extremity of Arnhem Land, from east of the Cobourg include Plumb (1963,1965), Rix (1964a, 1965), Dunnet Peninsula to the Wessel Islands and extending inland up (1965), Petroconsultants (1989), Bradshaw et al (1990), to about 80 km, are the only onshore manifestation of the McLennan et al (1990), Plumb and Roberts (1992), Rawlings basin. et al (1997), Carson et al (1999), Struckmeyer (2006a, b), The Arafura Basin succession is underlain by Palaeo- Totterdell (2006), Geoscience Australia (2008, 2012) and to Mesoproterozoic rocks of the McArthur Basin and Pine Zhen et al (2011). 130° 131° 132° 133° 134° 135° 136° 137° Mesozoic–Cenozoic 9° Indonesia Neoproterozoic–Palaeozoic Australia Palaeo–Mesoproterozoic basins (northern Arafura Basin) Palaeo–Mesoproterozoic orogens 10° Money Shoal Basin Archaean onshore Arafura Basin Bonaparte Basin (Goulburn Graben) Money Shoal Basin (Arafura Basin) offshore Arafura Basin (under cover) 11° road rail Carpentaria international border Basin 12° Nhulunbuy Jabiru locality Darwin Arafura Basin Jabiru Daly Basin 13° McArthur Arnhem Pine Creek Basin Carpentaria Province Orogen Basin 0300 kmNORTHERN TERRITORY A12-192.ai Figure 35.1. Regional geological setting of Arafura Basin (modi¿ed from Totterdell 2006, ¿gure 4). NT geological regions slightly modi¿ed from NTGS 1:2.5M geological regions GIS dataset. Offshore margins of basin after Petroconsultants (1989) and Totterdell (2006). Geology and mineral resources of the Northern Territory 35:1 Special publication 5 Arafura Basin NEOPROTEROZOIC TO ?EARLY CAMBRIAN: (Totterdell 2006, Figure 35.3, see Structure and tectonics). BASIN PHASE 1 The ¿ll of these half grabens and the overlying sag phase sedimentary rocks comprise the Wessel Group (Plumb et al Wessel Group 1976, Figure 35.2, 35.4), which is a succession of shallow marine, mostly quartz sandstone, mudstone and minor Deposition in the Arafura Basin commenced in the carbonate rocks. It is the only part of the basin, along with Neoproterozoic during a period of upper crustal extension the middle Cambrian Jigaimara Formation (basal Goulburn that resulted in the formation of a series of half grabens, Group), that is exposed onshore, where it reaches a composite which form an overall northeast-trending depocentre in thickness estimated to be about 2300 m (Rawlings et al the northern basin that continues into Indonesian waters 1997). Offshore, in the central part of the basin, it reaches A B Goulburn Graben northern Arafura Basin Kulka 1 W ESE 0 1 2 3 4 Two-way time (s) Two-way 5 6 0 25 km 7 A09-246.ai Money Shoal Basin Arafura Basin Cenozoic Late Carboniferous–Permian Neoproterozoic–?early Cambrian Woodbine Group equivalent Kulshill Group equivalent Wessel Group (sag phase) Cretaceous Late Devonian Wessel Group (rift phase) upper Bathurst Island Group Arafura Group Wessel Group and older Figure 35.2. Geoseismic cross- lower Bathurst Island Group Cambrian–Ordovician section through Arafura and Jurassic–Early Cretaceous Goulburn Group Basement Money Shoal basins (modi¿ed after Flamingo Group equivalent– Totterdell 2006, ¿gure 5). Location Troughton Group equivalent shown on Figure 35.7. 132°30' 133°30' 134°30' 135°30' 136°30' 137°30' 9°30' INDONESIA AUSTRALIA 5000 10°30' 4000 3000 2000 11°30' 1000 0 1000 2000 3000 12°30' TWT (ms) TWT 4000 5000 6000 NORTHERN 6473 TERRITORY 0 25 50 km A09-247.ai Figure 35.3. Arafura Basin Petroleum exploration well Normal fault sediment thicknesses (milliseconds dry, abandoned Thrust fault two-way time), showing signi¿cant oil show normal faults involved in graben oil/gas show Goulburn Graben development and location of oil indication drillholes (modi¿ed from Totterdell oil/gas indication 2006, ¿gure 6). Geology and mineral resources of the Northern Territory 35:2 Special publication 5 Arafura Basin a maximum thickness of about 10 000 m (Totterdell 2006). of 790 and 770 Ma, respectively, were determined for The group outcrops in an arcuate belt along the northwestern a single glauconite from the Elcho Island Formation at coastline of the Territory, from WESSEL ISLANDS- the top of the group (McDougall et al 1965). Plumb et al TRUANT ISLAND1, through northern and western (1976) reinterpreted the age of the entire Wessel Group as ARNHEM BAY, to eastern and northern MILINGIMBI Cambrian, based on the purported presence of Skolithos and JUNCTION BAY (Figure 35.5). It unconformably trace fossils in the Buckingham Bay Sandstone (Plumb overlies various formations of the McArthur Basin and 1963, Dunnet 1965), and the discovery of a middle is overlain, probably disconformably, by the Jigaimara Cambrian metazoan fauna in what was then considered Formation. The onshore Wessel Group comprises, in to be the Elcho Island Formation. However, Rawlings ascending order, the Buckingham Bay Sandstone, Raiwalla et al (1997) reinterpreted the Skolithos trace fossils as Shale, Marchinbar Sandstone and Elcho Island Formation abiogenic dewatering structures and assigned the metazoan (Table 35.1). These generally form an arcuate to linear fauna to the Jigaimara Formation. The discovery of the outcrop tract parallel to the preserved margins of the basin carbonaceous fossil Chuaria in the Raiwalla Shale (Haines with the younging direction northward towards the basin’s 1998) subsequently reaf¿rmed a Neoproterozoic age for the offshore depocentre. Seismic data indicate that the basal, group, although an early Cambrian age for the top of the offshore rift-¿ll succession of the group is not represented group cannot be discounted. in onshore areas (Totterdell 2006). The Wessel Group is probably equivalent in age to The age of the Wessel Group is poorly constrained Supersequence 3 and 4 rocks of the Centralian A Superbasin between underlying Mesoproterozoic basement rocks to the south (see &HQWUDOLDQ6XSHUEDVLQ¿JXUH).