gnt_ch35_arafura.pdf
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AhmadM and MunsonTJ (compilers)
Northern Territory Geological SurveySpecial Publication5
Chapter35: Arafura Basin
Geology and mineral resources
of the Northern Territory
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.
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35:1
Arafura Basin
Creek Orogen. To the west, it is unconformably overlain by
relatively undeformed Mesozoic and Cenozoic sedimentary
rocks of the Money Shoal Basin, which are up to 4.5 km
thick (Figure 35.2). This succession is continuous with that
of the Bonaparte Basin to the west, but thins rapidly to the
east, so as to form the onlapping edge of a vast Mesozoic
to Cenozoic depositional area that extends over much of
offshore northwestern Australia (Bradshaw et al 1990,
Struckmeyer 2006b). Mesozoic and Cenozoic sedimentary
rocks of the Carpentaria Basin onlap the Arafura Basin
to the east and southeast, and are up to 1760 m thick. The
northern limits of the Arafura Basin are not well dened,
although seismic data indicate that it extends towards
the Aru Ridge and Merauke Rise to the south of Papua,
Indonesia (Moss 2001). Palaeozoic sedimentary rocks are
also known from central Papua, indicating that the original
limits of the basin prior to Mesozoic tectonism may havebeen at least this far to the north (Fortey and Cocks 1986,
Nicoll and Bladon 1991). To the northwest, the poorlyexplored Barakan Basin in Indonesian waters is of similar
age and has a similar structure to that of the Arafura Basin
(Barber et al2004).
This chapter focuses on the onshore sedimentary
succession of the Arafura Basin in the NT. A full discussion
of the other components of the basin is beyond the scope
of this volume, although brief summaries of the offshore
successions are also included. Signicant studies of the
Arafura Basin and in particular, the onshore succession,
include Plumb (1963,1965), Rix (1964a, 1965), Dunnet(1965), Petroconsultants (1989), Bradshaw et al (1990),
McLennan et al (1990), Plumb and Roberts (1992), Rawlings
et al (1997), Carson et al (1999), Struckmeyer (2006a, b),
Totterdell (2006), Geoscience Australia (2008, 2012) and
Zhen et al (2011).
Chapter 35: ARAFURA BASIN M Ahmad and TJ Munson
INTRODUCTION
The Neoproterozoic to Permian Arafura Basin extends
from the onshore Northern Territory into Indonesian waters
(Figure 35.1) and covers an area of about 500 000 km2.
Structurally, the basin consists of northern and southern
sections separated by the large deformed Goulburn Graben
(Bradshaw et al 1990; equivalent to Arafura Graben of
Petroconsultants 1989). The Goulburn Graben is a west-
northwest-trending asymmetric feature, over 350 km long
and up to 70 km wide, that contains a sedimentary section
in excess of 10 km thick. The region to the north of the
Goulburn Graben forms the basins main depocentre and
contains a sedimentary succession up to 15 km thick
(Figures 35.2, 35.3). South of the Goulburn Graben a north-
dipping relatively undeformed ramp that extends onshore
contains up to 3 km of sedimentary rocks. The ArafuraBasin succession comprises sandstone, shale, limestone,
dolostone, coal beds and glacial deposits and is summarised
in Figure 35.4and Table 35.1. Totterdell (2006) described
four main phases of deposition within the basin (Basin
phases 14) in the Neoproterozoic (Wessel Group), middle
CambrianEarly Ordovician (Goulburn Group), Late
Devonian (Arafura Group) and Late CarboniferousEarly
Permian (Kulshill Group equivalent). These basin phases
were separated by long, relatively tectonically quiescent
periods of non-deposition and erosion. Neoproterozoic and
Cambrian sedimentary rocks, which outcrop on the northern
extremity of Arnhem Land, from east of the CobourgPeninsula to the Wessel Islands and extending inland up
to about 80 km, are the only onshore manifestation of the
basin.
The Arafura Basin succession is underlain by Palaeo-
to Mesoproterozoic rocks of the McArthur Basin and Pine
Current as of September 2012
0 300 km
Indonesia
Australia
MesozoicCenozoic
road
rail
PalaeoMesoproterozoic basins
PalaeoMesoproterozoic orogens
Archaean
onshore Arafura Basin
offshore Arafura Basin (under cover)
international border
locality
NeoproterozoicPalaeozoic
Darwin
Nhulunbuy
JabiruDaly Basin
Pine CreekOrogen
Money Shoal Basin
Money Shoal Basin
CarpentariaBasin
Arafura Bas in
McArthurBasin
ArnhemProvince
133 135 137131130 132 134 136
13
11
12
10
9
A12-192.ai
(northern Arafura Basin)
(Goulburn Graben)
(Arafura Basin)
Bon
apart
eBasin
CarpentariaBasin
Jabiru
NORTHERNTERRITORY
Figure 35.1. Regional geological setting of Arafura Basin (modied from Totterdell 2006, gure 4). NT geological regions slightly modiedfrom NTGS 1:2.5M geological regions GIS dataset. Offshore margins of basin after Petroconsultants (1989) and Totterdell (2006).
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Arafura Basin
35:2
NEOPROTEROZOIC TO ?EARLY CAMBRIAN:
BASIN PHASE 1
Wessel Group
Deposition in the Arafura Basin commenced in the
Neoproterozoic during a period of upper crustal extension
that resulted in the formation of a series of half grabens,
which form an overall northeast-trending depocentre in
the northern basin that continues into Indonesian waters
(Totterdell 2006, Figure 35.3, see Structure and tectonics).
The ll of these half grabens and the overlying sag phase
sedimentary rocks comprise the Wessel Group (Plumb et al
1976, Figure 35.2, 35.4), which is a succession of shallow
marine, mostly quartz sandstone, mudstone and minor
carbonate rocks. It is the only part of the basin, along with
the middle Cambrian Jigaimara Formation (basal Goulburn
Group), that is exposed onshore, where it reaches a composite
thickness estimated to be about 2300 m (Rawlings et al
1997). Offshore, in the central part of the basin, it reaches
0 25 km
northern Arafura Basin
Two-waytime(s)
Goulburn Graben
W ESE
BA
Kulka 1
0
1
2
3
4
5
6
7
Wessel Group and older
Wessel Group (rift phase)
Wessel Group (sag phase)
Neoproterozoic?early Cambrian
CambrianOrdovician
Late Devonian
Late CarboniferousPermianCenozoic
Cretaceous
JurassicEarly Cretaceous
Woodbine Group equivalent
upper Bathurst Island Group
lower Bathurst Island Group
Flamingo Group equivalent
Troughton Group equivalent
Arafura BasinMoney Shoal Basin
Goulburn Group
Arafura Group
Basement
Kulshill Group equivalent
A09-246.ai
A09-247.ai
dry, abandoned
Petroleum exploration well Normal fault
Thrust fault
Goulburn Graben
oil show
oil/gas show
oil indication
oil/gas indication
NORTHERN
TERRITORY
1000
2000
3000
4000
5000
INDONESIAAUSTRALIA
13230' 13330' 13430' 13530' 13630' 13730'
930'
1030'
1130'
1230'
1000
2000
3000TWT(ms)
4000
5000
60006473
0
0 25 50 km
Figure 35.2. Geoseismic cross-section through Arafura andMoney Shoal basins (modied afterTotterdell 2006, gure 5). Locationshown on Figure 35.7.
Figure 35.3. Arafura Basinsediment thicknesses (milliseconds
two-way time), showing signicantnormal faults involved in grabendevelopment and location ofdrillholes (modied from Totterdell2006, gure 6).
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Arafura Basin
a maximum thickness of about 10 000 m (Totterdell 2006).
The group outcrops in an arcuate belt along the northwestern
coastline of the Territory, from WESSEL ISLANDS-
TRUANT ISLAND1, through northern and western
ARNHEM BAY, to eastern and northern MILINGIMBI
and JUNCTION BAY (Figure 35.5). It unconformably
overlies various formations of the McArthur Basin and
is overlain, probably disconformably, by the Jigaimara
Formation. The onshore Wessel Group comprises, in
ascending order, the Buckingham Bay Sandstone, Raiwalla
Shale, Marchinbar Sandstone and Elcho Island Formation
(Table 35.1). These generally form an arcuate to linear
outcrop tract parallel to the preserved margins of the basin
with the younging direction northward towards the basins
offshore depocentre. Seismic data indicate that the basal,
offshore rift-ll succession of the group is not represented
in onshore areas (Totterdell 2006).
The age of the Wessel Group is poorly constrained
between underlying Mesoproterozoic basement rocks
and the overlying middle Cambrian Jigaimara Formation
(Goulburn Group). It was originally considered to beNeoproterozoic after Rb-Sr and K-Ar minimum dates
1 Names of 1:250 000 mapsheets are in large capital letters, egMILINGIMBI.
of 790 and 770 Ma, respectively, were determined for
a single glauconite from the Elcho Island Formation at
the top of the group (McDougall et al 1965). Plumb et al
(1976) reinterpreted the age of the entire Wessel Group as
Cambrian, based on the purported presence of Skolithos
trace fossils in the Buckingham Bay Sandstone (Plumb
1963, Dunnet 1965), and the discovery of a middle
Cambrian metazoan fauna in what was then considered
to be the Elcho Island Formation. However, Rawlings
et al (1997) reinterpreted the Skolithos trace fossils as
abiogenic dewatering structures and assigned the metazoan
fauna to the Jigaimara Formation. The discovery of the
carbonaceous fossil Chuariain the Raiwalla Shale (Haines
1998) subsequently reafrmed a Neoproterozoic age for the
group, although an early Cambrian age for the top of the
group cannot be discounted.
The Wessel Group is probably equivalent in age to
Supersequence 3 and 4 rocks of the Centralian A Superbasin
to the south (see ).
Buckingham Bay SandstoneThe Buckingham Bay Sandstone (Plumb and Roberts 1992)
unconformably overlies various units of the McArthur Basin
and is overlain conformably by the Raiwalla Shale. The
formation outcrops in a broad gently dipping arc around
Neoproterozoic
Ord
Devonian
Permian
GroupSeries/Stage
Period
TroughtonGp
equivalent/
FlamingoGp
equivalent/
BathurstIsland
Group
Cretaceous
Jurassicearly
Cretaceous
Car
Permian
MoneyS
hoalBasin
ArafuraBasin
Arafura
Group
GoulburnGroup
WesselGroup
ArafuraBasin
Car
Cretaceous
Period
Series/Stage
GroupFormation
middle
late
Darbilla Fm
Yabooma Fm
Djabura Fm
Mooroongga Fm
Milingimbi Fm
NaningburaDolomite
ElchoIsland Fm
MarchinbarSandstone
RaiwallaShale
OnshoreOutcrop
Goulburn-1
TD 1300
TD 3635
TD 2758
TD 2720
TD 3998
Arafura-1
Torres-1Tasman-1
1802
2540
3095
2275
1895
1295
1162
653
694.5
1074
1409
1704
1835
1998
3126
3596
1146
977
776
455
183
783
1450
1590
2058
2157
1188
Kulka-1
Buckingham
BaySandstone
Tremadocian
Floian
Frasnian?
Fammennian
(Strunian)
Pennsylvanian
Cisuralian
Pennsylvanian
Cisuralian400.5
JigaimaraFormation
KulshillGroup
equivalent
KulshillGroup
equivalent
Cambrian
??
?
A12-184.ai
0
1000
Depth (m)
Claystone
Siltstone
Shale
Sandstone
Limestone
Dolostone
Unconformity
Figure 35.4. Arafura Basin stratigraphic succession, showing correlations from offshore wells and onshore outcrop in the ArafuraBasin (modied from Bradshaw et al1990, gure 10). Money Shoal Basin stratigraphic succession after Geoscience Australia (2012).Abbreviations: Car = Carboniferous; Fm = Formation; Gp = Group; Ord = Ordovician; TD = total depth.
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Arafura Basin
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the margin of the onshore Arafura Basin in southwestern
JUNCTION BAY, MILINGIMBI, ARNHEM BAY and
southeastern WESSEL ISLANDS (Figure 35.5), and
is best exposed near the coast of Flinders Peninsula and
adjacent islands, with exposures becoming more broken and
disintegrating into sand inland (Rawlings et al1997, Carson
et al 1999). In the absence of a complete section through the
formation, Plumb and Roberts (1992) nominated a reference
area on the northwestern side of Flinders Peninsula around the
mouth of the Kurala River. The formation is estimated to be
about 350 m thick near its type locality (Rawlings et al1997).
The basal unit consists of massive to at-bedded, cross-
bedded, and occasionally rippled, medium- to coarse-
grained and sometimes pebbly, medium- to very thickly
bedded, white to pale pink and yellow (with local red
iron-oxide staining) sandstone. A local basal breccia or
Unit, max thickness,(distribution)
LithologyDepositionalenvironment
Stratigraphic relationships
CarboniferousPermian
KULSHILL GROUP EQUIVALENT
5000 m (offshore) Interbedded sandstone, siltstone and claystone,with minor coal, and dolomitic rocks; palynoora.
Fluvial to marginalmarine to shallowmarine.
Unconformable on Arafu ra Groupsuccession. Unconformably overlain byJurassicCenozoic Money Shoal Basinsuccession.
Late Devonian
ARAFURA GROUP
Darbilla Formation,380 m (offshore)
Mudstone, sandy siltstone and lesser interbeddedsandstone; includes ning-upward intervals;palynoora.
Non-marine,possibly sabkha ortidal at, and uvial.
Apparently conformable on YaboomaFormation. Unconformably overlain byJurassic Money Shoal Basin succession.
Yabooma Formation,335 m (offshore)
Interbedded siltstone with dolomitic intervals,occasional thin sandstone beds; sparse fossil faunaof conodonts, sh and bryozoans.
Nearshore shallowmarine.
Unconformable on Djabura Formation.Apparently conformably overlain by DarbillaFormation, or unconformably overlain byJurassic Money Shoal Basin succession.
Djabura Formation,466 m (offshore)
Interbedded, mudstone, siltstone, sandstone andminor carbonate rocks; diverse fossil fauna,including conodonts, ostracods, phosphaticbrachiopods, conulari ids and sh fossils;palynoora.
Nearshore shallowmarine.
Unconformable on Goulburn Groupsuccession. Unconformably overlain byYabooma Formation, or by Kulshill Groupequivalent.
middle Cambrian to Early Ordovician
GOULBURN GROUP
Mooroongga Formation,201 m (offshore)
Shale, limestone, sandstone, glauconitic sandstone,minor chert, dolomitic in part; becomes morecalcareous up-section; limited conodont fauna.
Shallow marine. Probably conformable on MilingimbiFormation.
Milingimbi Formation,169 m (offshore)
Dolostone, limestone, glauconitic sandstone, shale;becomes more siliciclastic up-section; conodontfaunas.
Shallow marine. Conformable on Naningbura Dolomite.Probably conformably overlain byMooroongga Formation, or unconformablyoverlain by Arafura Group.
Naningbura Dolomite
1128 m (offshore)Dolostone with silty dolostone intervals; conodontfauna near top.
Shallow marine. Apparently conformable on JigaimaraFormation.
Jigaimara Formation
470 m (offshore andonshore)
White to grey interbedded limestone, shale anddolostone, silicied to chert and brecciated;possible microbial laminations; rich fossil faunaof trilobites, bradoriids, hyoliths, lingulatebrachiopods and sponge spicules.
Low-energy, shallowmarine, probablysubtidal.
Disconformable or unconformable on ElchoIsland Formation.
Neoproterozoic to ?early Cambrian
WESSEL GROUP
Elcho Island Formation
650700 m (onshore)
Fine- to coarse-grained, thinly to medium bedded
sandstone, often calcareous or dolomitic andlocally glauconitic, with cross-beds, ripples,current lineations and load casts; minor mudstoneinterbeds; occasional carbonate intervals, locallystrongly leached or silicied to chert breccia
Shallow marine,
occasional exposed;periodic evaporiticconditions.
Locally disconformable or possibly
conformable on Marchinbar Sandstone.
Marchinbar Sandstone
300 m (onshore)White, quartz-rich, ne- to medium-grainedsandstone, mostly medium bedded, with horizontallaminations, trough cross-beds, wave and currentripples, rare desiccation cracks.
Relatively high-energy very shallowmarine.
Conformable and gradational on RaiwallaShale.
Raiwalla Shale
1000 m (onshore)Grey and green micaceous mudstone, red-brownwhen weathered, interbedded with ne- tomedium-grained tabular sandstone.
Subtidal marineshelf, gradualupward shallowingwith increasingstorm inuence.
Conformable with sharp contact onBuckingham Bay Sandstone.
Buckingham BaySandstone350 m (onshore)
White, grey, pale pink, yellow and red, ne-to coarse-grained, mostly medium to thicklybedded sandstone, with common cross-beds andoccasionally ripples; rare mudstone interbeds;local basal breccia and conglomerate.
High-energyshallow marine.
Unconformable on McArthur Basinsuccession.
Table 35.1. Summary of Palaeozoic stratigraphic succession of the Arafura Basin.
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Arafura Basin
conglomerate, up to several metres thick, contains poorly
sorted angular clasts up to boulder size in a sandstone
matrix (Rawlings et al 1997). Higher in the succession,
pale grey, medium-grained, thickly bedded, massive to
weakly at-bedded sandstone is interbedded with recessive,
ferruginous and micaceous, thinly bedded, ne-grained
sandstone and mudstone. Near the top of the formation, the
lithology tends to be more uniform, comprising medium-
grained, medium- to thickly bedded sandstone, varying
from white to red and yellow with weathering. No metazoan
fossils have been found in the Buckingham Bay Sandstone
and purported Skolithos trace fossils recorded by Plumb
(1963) and Dunnet (1965), and used to suggest a Cambrian
age for the entire Wessel Group by Plumb et al(1976), were
subsequently interpreted as having been caused by the
dewatering of uidised sand, and are therefore abiogenic
(Rawlings et al1997).
The Buckingham Bay Sandstone is interpreted to
have been deposited in a high-energy shallow marine
environment. The formation probably correlates with
the similar Bukalara Sandstone of the central northernGeorgina Basin, which unconformably overlies the southern
McArthur Basin succession (Pietsch et al1991).
Raiwalla Shale
The Raiwalla Shale (Plumb and Roberts 1992) outcrops
poorly in a broad arcuate belt through MILINGIMBI and
ARNHEM BAY (Figure 35.5). It overlies the Buckingham
Bay Sandstone with a sharp concordant contact and is
overlain conformably and gradationally by the Marchinbar
Sandstone. The formation comprises mudstone with very
ne- to medium-grained tabular sandstone interbeds
(Rawlings et al 1997). The lower mudstone-rich part of
the formation is very recessive and is poorly exposed.
Sandstone scree dominates most surface exposures, so that
it is difcult to determine the ratio of sandstone to shale.
Better exposures in the upper half of the formation probably
reect an increasing proportion of sandstone interbeds up-
section. An accurate thickness cannot be determined for
the formation due to very shallow dips and the poor nature
of outcrop, but it is estimated to be of the order of 1000 m
(Rawlings et al1997). Plumb and Roberts (1992) nominated
a reference area for the formation around the Woolen River
in ARNHEM BAY.
Mudstone is micaceous, at- to wavy-laminated andssile (shaly). Sandstone varies from quartz-rich to lithic
to micaceous, is ne- (dominant) to medium-grained, and
JUNCTION BAY WESSEL ISLANDS
MILINGIMBI ARNHEM BAY
TRUANT ISLAND
GOVE
ARNHEM BAY
0 50 100 km
MesozoicCenozoic locality
bauxite occurrence
iron ore occurrence
250k mapsheet
PalaeoMesoproterozoicbasins
PalaeoMesoproterozoicorogens
NeoproterozoicPalaeozoic
Jigaimara Fm
Marchinbar Sst
Raiwalla Shale
Wessel Group
Neoproterozoic?early Cambrian
Neoproterozoic
Buckingham
Bay Sst
Elcho Island Fm
A12-193.ai
NORTHERN
TERRITORY
Maningrida
Elcho
Milingimbi
Goomadeer
River
Riv
er
Man
n
Live
rpool
Riv
er
River
Blyth
Cad
ell
River
River
River
Goy
der
Riv
er
River
Glyde
Woolen
Gulbu
wanga
y
Milingimbi
Maningrida
Galiwinku
Raiwalla Shale
Jigaimara Fm
Elcho
Elcho North
Elcho South
Easy
Able
Red Cliff
Dog
Sphinx Head
Fox
Truant Island
Baker
Milingimbi
Probable Island
Figure 35.5. Onshore Arafura Basin, showing simplied geology of Wessel Group and Jigaimara Formation (basal Goulburn Group),derived from GA 1:1M geology and NTGS 1:2.5M geological regions GIS datasets. Locations of mineral occurrences are from NTGSMineral Occurrence Database (MODAT). Fm = Formation; Sst = Sandstone.
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Arafura Basin
35:6
is thinly to medium bedded, with a few packets containing
thicker beds. The sandstone typically displays at- to wavy-
and some cross-lamination, and wave and current ripples
are common on bed tops. Synaeresis cracks and mudclasts
are also common, and soft-sediment deformation features
are present locally. Small (millimetre-sized) iron-oxide
inclusions, which are locally abundant, suggest that some
intervals of the formation are pyritic in the subsurface.
No metazoan or t race fossils have been recorded from the
Raiwalla Shale, but carbonaceous impressions assigned to
Chuariahave been used to assign a Neoproterozoic age to
the unit (Haines 1998).
The Raiwalla Shale was probably deposited under
subtidal, marine shelf conditions (Rawlings et al 1997).
The basal contact is probably a marine ooding surface and
represents a rapid deepening from the very shallow water
conditions interpreted for the Buckingham Bay Sandstone.
There is evidence for gradual upward shallowing with
increasing storm inuence through the succession
(Rawlings et al1997). The Raiwalla Shale is correlated with
the Cox Formation of the central northern Georgina Basin;this unit overlies the Bukalara Sandstone, an equivalent of
the Buckingham Bay Sandstone (Pietsch et al1991).
Marchinbar Sandstone
The Marchinbar Sandstone conformably and gradationally
overlies the Raiwalla Shale and outcrops in a relatively linear
belt through western TRUANT ISLAND, southeastern
WESSEL ISLANDS, northwestern ARNHEM BAY and
eastern MILINGIMBI (Figure 35.5). It was dened by
Plumb and Roberts (1992), who nominated a reference
section on Marchinbar Island in WESSEL ISLANDS.
The formation generally outcrops poorly, with exposurescommonly restricted to places where creeks have eroded
through the regional laterite capping. It is an estimated
300 m thick in the vicinity of the Woolen River (ARNHEM
BAY), where the most complete exposed section is located
(Rawlings et al 1997). The upper contact with the Elcho
Island Formation is regionally concordant, but at the only
locality where the actual point of contact can be seen, the
boundary is erosional and marked by a thin granule and
pebble lag, suggesting the possibility of at least a local
disconformity at this level (Rawlings et al1997).
The Marchinbar Sandstone is composed largely of clean,
white quartz sandstone, which is dominantly medium-
grained, but which includes some ne-grained beds,mainly near the base. Thin red, ferruginous and matrix-
rich intervals are a minor component of the formation.
Mudclasts are very common near the base, but decrease in
abundance upwards. Most of the unit is medium-bedded,
although more thinly and thickly bedded intervals are
also present. Sedimentary structures include common
horizontal lamination, trough cross-bedding, wave and
current ripples, and rare desiccation cracks (Rawlings et al
1997). No metazoan or trace fossils have been found in the
formation and its interpreted Neoproterozoic age is based
entirely on its stratigraphic position (Zhen et al 2011). A
relatively high-energy very shallow marine environment isinterpreted for the unit and it probably represents the top
of a shoaling cycle that began in the lower Raiwalla Shale
(Rawlings et al1997).
Elcho Island Formation
The Elcho Island Formation outcrops extensively in
southern WESSEL ISLANDS, northwestern ARNHEM
BAY and northeastern MILINGIMBI (Figure 35.5), along
the coasts of northern Arnhem Land and Elcho, Howard
and Banyan islands, and it is also sparsely exposed inland
above the slightly more resistant Marchinbar Sandstone. It
was dened by Plumb and Roberts (1992), who nominated
a reference section as cliff outcrops on Elcho Island, but
was redened in Rawlings et al (1997), who nominated a
type locality in western ARNHEM BAY. The formation is
at least locally disconformable, or possibly conformable on
the Marchinbar Sandstone and is probably disconformably
overlain by the Jigaimara Formation of the Goulburn Group.
A thickness of 650700 m is estimated for the Woolen River
area (Rawlings et al1997).
The Elcho Island Formation is a succession of ne- to
coarse-grained, locally glauconitic, thinly to medium-bedded
sandstone, generally interbedded with minor mudstone and
chert. Sedimentary structures include trough and tabular
cross-beds, wave and current ripples (Figure 35.6a), currentlineations and load casts. The succession is sometimes
calcareous or dolomitic, and chert breccia and leached rocks
after carbonate are present locally. The age of the formation is
poorly constrained between the Neoproterozoic lower Wessel
Group and the middle Cambrian Jigaimara Formation, but
a Neoproterozoic age is more likely from the absence of
metazoan or trace fossils, and from radiometrically dating of
a single glauconite from low in the Elcho Island Formation
(McDougall et al1965) at about 770 Ma (K-Ar) and 790 Ma
(Rb-Sr). The Elcho Island Formation was deposited under
shallow marine shelf conditions, which at times, reached the
point of exposure and desiccation (Figure 35.6b). Periodicevaporitic conditions are indicated by halite pseudomorphs
and desiccation cracks near the base and top.
MIDDLE CAMBRIAN TO EARLY ORDOVICIAN:
BASIN PHASE 2
Goulburn Group
The early middle CambrianEarly Ordovician Goulburn
Group (Petroconsultants 1989, McLennan et al 1990,
Bradshaw et al 1990, Nicoll et al 1996, Rawlings et al 1997)
disconformably or unconformably overlies the Wessel
Group and is unconformably overlain by the Late DevonianArafura Group. It has sag- to sheet-like geometry and is
structurally conformable with the upper, post-rift portion
of the Wessel Group. The succession reaches a maximum
thickness of about 2000 m in the offshore central part of
the northern Arafura Basin and contains, in ascending
order, the Jigaimara Formation, Naningbura Dolomite,
Milingimbi Formation and Mooroongga Formation.
The basal part of the Jigaimara Formation is exposed in
southern WESSEL ISLANDS, northwestern ARNHEM
BAY and northeastern MILINGIMBI (Figure 35.5),
but the upper part of the unit and the other formations
are only intersected in petroleum exploration drillholesin the Arafura Sea (Figure 35.4). The Goulburn Group
represents prolonged deposition on a shallow marine shelf
in a stable intraplate setting.
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Arafura Basin
The age of the Goulburn Group has been established
from the presence of a middle Cambrian marine fauna in
the basal Jigaimara Formation and from Early Ordovician
conodont faunas in the Milingimbi and Mooroongga
formations (Zhen et al 2011). In offshore drillhole Money
Shoal-1, unnamed and poorly dated ?Cambrian strata (from
25302575 m) contain interbedded andesitic volcanic rocks,
indurated ne- to medium-grained arkosic sandstone, and
dark grey-green to black carbonaceous shale. The volcanic
rocks might be stratigraphic equivalents of the Antrim
Plateau Volcanics (Brown et al 1968, Petroconsultants
1989, see Kalkarindji Province) and if so, then a late early
Cambrian age is possible for the base of the group.
Jigaimara Formation
The Jigaimara Formation (Haines in Rawlings et al 1997)
disconformably or unconformably overlies the Elcho Island
Formation and is apparently conformably overlain by the
Naningbura Dolomite (Rawlings et al 1997, Zhen et al
2011). It is a succession of interbedded limestone, shale and
dolostone that is exposed at Warnga Point on Elcho Island andon several small islands north and northeast of Milingimbi
township (Figure 35.5). Exposures are scattered and nearly
at-lying, and individual sections are only a few metres
thick. The rocks are silicied and consist of white to grey-
brown chert (presumably after limestone and calcareous
siltstone). They are invariably brecciated to various degrees
(jigsaw t to totally chaotic) and have a siliceous matrix.
Individual clasts are commonly well laminated and possible
microbial laminations are also present, as are enigmatic
doughnut-shaped ?algal structures, about 20 cm in diameter
(Rawlings et al 1997, Carson et al 1999). The formation
reaches a maximum thickness of 470 m in offshore drillholeArafura-1 (Zhen et al 2011).
The Jigaimara Formation is very fossiliferous and
contains a fauna of trilobites, bradoriids, hyoliths, lingulate
brachiopods and sponge spicules at its base; this fauna
is most likely to be middle to late Templetonian (early
middle Cambrian) in age (Shergold in Plumb et al 1976,
Laurie 2006a, b, Zhen et al 2011). The age of the top of the
formation is constrained by the apparently conformably
overlying Naningbura Dolomite, which is Furongian2 (late
Cambrian) to early Tremadocian (Early Ordovician). The
Jigaimara Formation is therefore Templetonian?Mindyallan
in age and can be correlated with sequence 2 (latest Ordian
early Mindyallan) of the Centralian B Superbasin. Thisis the second of two successive widespread sedimentary
successions, characterised by distinctive invertebrate faunas,
that have been recognised in central and northern Australia
from sequence stratigraphic studies of middle Cambrian strata
in the Georgina Basin (Shergold et al 1988, Southgate and
Shergold 1991, Laurie 2006c, see Centralian Superbasin:
). The Jigaimara Formation was deposited in low-
energy, shallow marine, probably subtidal settings, following
a regional transgression (Rawlings et al1997).
Naningbura Dolomite
In offshore drillhole Arafura-1, the Naningbura Dolomiteis a thick largely dolostone succession with silty dolomitic
2 Corresponds to the IdameanDatsonian Australian stages.
intervals that was deposited in a predominantly shallow
marine environment. It is apparently conformable between
the Jigaimara Formation (below) and the Milingimbi
Formation, and is equivalent to units O1 to O7 of
Petroconsultants (1989). Nicoll et al (1996) originally named
this unit the Naningbura Formation, but it was not dened
and only briey described. The Naningbura Formation
was subsequently mentioned in Rawlings et al (1997),
Carson et al (1999) and Struckmeyer (2006b), but none
of these publications provided enough detail to properly
establish the unit with this name. Nicoll (2006a) renamed
the unit the Naningbura Dolomite, allocated a type section
Figure 35.6. Elcho Island Formation. (a) Megaripples on wave-cutplatform (near 561200mE 8671600mN, Galiwinku, Elcho Island,after Rawlings et al 1997, plate 34). (b) Desiccation cracks insandstone at top of unit (522300mE 8647500mN, Banyan Island,after Rawlings et al 1997: plate 35).
a
b
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in Arafura-1, and provided a more detailed description
of its lithologies, distribution and conodont fauna. This
name was also used by Zhen et al (2011), who provided
detailed descriptions of the conodont palaeontology and
biostratigraphic succession. These publications rmly
establish the name of the unit as Naningbura Dolomite
and this nomenclature is followed herein. The Naningbura
Dolomite is 1128 m thick in the type section in Arafura-1,
the only drillhole to penetrate the entire unit (Figure 35.4).
Incomplete thicknesses intersected in other drillholes are in
the range 154601 m. A conodont fauna recovered from the
top of the unit is late Furongian to early Tremadocian in age
(Nicoll 2006a, Zhen et al 2011), but the undated base of the
unit may be as old as middle Cambrian.
Milingimbi Formation
The Milingimbi Formation (Bradshaw et al 1990, Nicoll
2006a) corresponds to units O8 and O9 of Petroconsultants
(1989). It is conformable on the Naningbura Dolomite
and is probably conformably overlain by the Mooroongga
Formation, or is unconformably overlain presumablyby the Late Devonian Arafura Group (Zhen et al 2011).
The formation is of mixed lithology and comprises silty
dolostone to limestone, glauconitic sandstone and shale,
deposited predominantly in a shallow marine environment
(Nicoll 2006a, Zhen et al 2011). The lower part of the
Milingimbi Formation is dolomitic, but it becomes more
siliciclastic up-section, where thin glauconitic sandstone is
interbedded with dolostone, limestone and shale (Bradshaw
et al1990). In the type section in drillhole Arafura-1, the
Milingimbi Formation is 163 m thick and in Goulburn-1, the
unit is 169 m thick. Pre-Devonian erosion has truncated the
formation in Torres-1, where it is only 95 m thick, and hascompletely removed the unit in Tasman-1 (Figure 35.4).
Conodont faunas of Tremadocian (Early Ordovician) age
have been described from the unit (Bradshaw et al 1990,
Zhen et al2011).
Mooroongga Formation
The Mooroongga Formation (Bradshaw et al 1990, Nicoll
2006a) corresponds to units O10 to O133of Petroconsultants
(1989). It is probably conformable on the Milingimbi
Formation, but a major unconformity separates this unit
from the overlying Upper Devonian Djabura Formation
(Arafura Group). The Mooroongga Formation comprises
shale and interbedded limestone with some thin sandstoneinterbeds and minor chert, and becomes more calcareous
upward. Glauconite is common and parts of the formation
are dolomitic (Zhen et al 2011). The depositional setting
was predominantly shallow marine (Zhen et al2011). The
Mooroongga Formation is 131 m thick in Arafura-1, 201 m
thick in Goulburn-1 and has been completely removed by
erosion in Tasman-1 and Torres-1 (Nicoll 2006a, Zhen et al
2011, Figure 35.4). Petroconsultants (1989) reported the
presence of conodonts, ostracods, sh remains, conulariids,
echinoderms, inarticulate brachiopods, gastropods,
?tentaculitids and sponge spicules from this unit. The
3 Petroconsultants (1989) did not describe Unit O13, but didinclude it in Geological cross-section AA1 Arafura Basin. Itonly occurs in Goulburn-1.
formation is considered to be of early Floian (late Early
Ordovician) age, based on the limited, but diagnostic
conodont fauna (Zhen et al2011), and is about the same age
as the late Tremadocian to Floian Florina Formation of the
Daly Basin.
LATE DEVONIAN: BASIN PHASE 3
Arafura Group
The Upper Devonian Arafura Group (Petroconsultants
1989, Bradshaw et al 1990, McLennan et al 1990)
unconformably overlies units of the Goulburn Group.
A hiatus of about 100 million years separates the two
groups which are generally structurally conformable. The
Arafura Group consists of shallow marine to non-marine
interbedded mudstone, siltstone, sandstone and minor
carbonate rocks. It has sag to sheet-like geometry in the
northern Arafura Basin, where it is about 1500 m thick,
but the geometry of the group is more complex within the
Goulburn Graben (Totterdell 2006). Bradshaw et al (1990)divided the Arafura Group into the Djabura, Yabooma and
Darbilla formations. It is unconformably overlain by strata
equivalent to the Upper CarboniferousLower Permian
Kulshill Group of the Bonaparte Basin, or where these are
absent, by Jurassic strata of the Money Shoal Basin.
Djabura Formation
The Djabura Formation (Bradshaw et al 1990) has been
intersected in Tasman-1, Torres-1, Arafura-1 and Goulburn-1
(Figure 35.4) and is equivalent to units D1 D4 of
Petroconsultants (1989). It unconformably overlies various
Cambrian and Ordovician units of the Goulburn Group andis unconformably overlain by the Yabooma Formation, or by
younger (Upper Carboniferous) Kulshill Group equivalent
sedimentary rocks (Nicoll 2006b). It ranges in thickness
from 295 m to 466 m, and consists of interbedded, mudstone,
siltstone, sandstone and minor carbonate rocks, which were
deposited in a nearshore shallow marine environment (Nicoll
2006b, Totterdell 2006). Diverse marine fossils, including
conodonts, ostracods, phosphatic brachiopods, conulariids
and sh fossils, are found throughout the unit. The conodonts
indicate an early Famennian age for the formation (Nicoll
2006b), but palynological dating suggests it is slightly older
(Frasnian; Purcell 2006).
Yabooma Formation
The Yabooma Formation (Bradshaw et al 1990) is
equivalent to the interval from unit D5 to the lower part
of unit D7 of Petroconsultants (1989). It unconformably
overlies the Djabura Formation and is intersected
in drillholes Torres-1, Arafura-1 and Goulburn-1
(Figure 35.4). It is apparently conformably overlain by
the Darbilla Formation, or is unconformably overlain by
Jurassic sediments of the Money Shoal Basin (Bradshaw
et al1990, Nicoll 2006b). It ranges in thickness from 140
to 335 m, and is predominantly composed of interbedded
siltstone with dolomitic intervals and occasional thinsandstone beds. A relatively sparse fossil fauna includes
conodonts, sh and bryozoan fragments recovered in
cuttings from Goulburn-1. The conodont fauna is from
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Arafura Basin
the base of the formation and indicates a late Famennian
age (Nicoll 2006b). The Yabooma Formation is interpreted
to represent predominantly nearshore shallow marine
deposition (Bradshaw et al1990, Totterdell 2006).
Darbilla Formation
The Darbilla Formation (Bradshaw et al1990) is equivalent
to the upper part of unit D7 and unit D8 of Petroconsultants
(1989). It has only been intersected in Arafura-1 and
Torres-1 (Figure 35.4), where it is 380 m and 262 m thick,
respectively. The unit is apparently conformable on the
Yabooma Formation and is overlain unconformably by
Jurassic strata of the Money Shoal Basin. The formation is
composed mostly of mudstone, sandy siltstone and lesser
interbedded sandstone, and includesning-upward intervals.
It does not contain marine fossils and is interpreted to
represent a largely non-marine regression (Petroconsultants
1989, Bradshaw et al1990, Nicoll 2006b, Totterdell 2006).
Possible sabkha or tidal at and uvial depositional settings
were suggested by Petroconsultants (1989). A palynoora
from the base of the Darbilla Formation indicates a latestFamennian (uppermost Strunian sub-stage) age for the
unit (Nicoll 2006b).
LATE CARBONIFEROUSEARLY PERMIAN:
BASIN PHASE 4
Kulshill Group equivalent
The Arafura Group is unconformably overlain by a Late
CarboniferousEarly Permian sedimentary succession that
is approximately equivalent in age to the Kulshill Group
of the Bonaparte Basin (Totterdell 2006). Kulshill Groupequivalent rocks reach a maximum thickness of about
5000 m in the Goulburn Graben, which was formed at this
time, but the original thickness of the group was probably
much greater, as it is interpreted that up to 3000 m of
section has been eroded following deformation and uplift
in the Triassic (Struckmeyer et al2006). The lower part of
the group thickens into the bounding planar normal faults
of the graben (Figure 35.2), indicating that it was a part of
the rift succession. However, the upper part does not exhibit
any noticeable divergence into the faults and is therefore
considered to represent post-rift deposition. Kulshill Group
equivalent rocks to the north of the Goulburn Graben
have a sag to sheet-like geometry and a relatively uniformthickness (maximum 3000 m), except where eroded around
the margins of the basin. They are structurally conformable
with the underlying rocks and are also interpreted to be
part of the post-rift succession. Seismic and magnetic data
indicate that there was some magmatic activity in the basin
during the rifting phase that resulted in the emplacement
of sills and dykes, and a large magmatic body within the
Goulburn Graben (Totterdell 2006). A dolerite intersected
in drillhole Kulka-1 has been dated by K-Ar method at
293 3 Ma (Bradshaw et al 1990).
The Kulshill Group equivalent succession comprises
interbedded sandstone, siltstone and claystone, with minorcoal, and dolomitic rocks (Totterdell 2006). These were
deposited in a variety of environments ranging from uvial
to marginal marine to shallow marine (Petroconsultants
1989). Palynological studies by Helby (2006) show that
that this interval spans the Pennsylvanianmid-Cisuralian
APP11 to APP122 palynooral zones of Price (1997), but
most of the succession is Early Permian in age and only
the basal 100 m corresponds to the Late Carboniferous.
Petroconsultants (1989) divided the succession in several
drillholes into four unnamed units and correlated these with
the Tanmurra Formation, Point Spring Sandstone, Kuriyippi
Formation and Treachery Formation of the Bonaparte
Basin. However, improved dating of the succession shows
that a better correlation is with units from the younger
interval Kuriyippi Formationlower Keyling Formation
(see ).
The Kulshill Group equivalent succession is separated
by a major unconformity from overlying strata of the
Jurassic to Cenozoic Money Shoal Basin (Figure 35.2).
In contrast to Arafura Basin strata, which are complexly
faulted and folded, the Money Shoal Basin succession is
generally undisturbed.
STRUCTURE AND TECTONICS
The Arafura Basin was initiated in the Neoproterozoic
as a result of northwestsoutheast-directed upper crustal
extension that produced a series of northeastsouthwest-
trending half grabens across the basin. The subsidence
history was episodic, limited to four periods of basin-
wide subsidence (Basin phases 14) separated by long,
relatively tectonically quiescent periods of non-deposition
and erosion. Minor localised deformation in the Devonian
and Carboniferous was probably due to the effect of far-
eld stresses associated with the Alice Springs Orogeny
(Totterdell 2006). The WNWESE-trending GoulburnGraben (Figures 35.2, 35.3, 35.7) was formed in the Late
Carboniferous to Early Permian, in response to oblique
extension, and underwent oblique inversion in the Triassic
during a phase of regional contractional deformation (Basin
phase 5 of Totterdell 2006). The main deformations events
that have affected the basin are discussed below, in ascending
date order.
Neoproterozoic extensional faulting
Neoproterozoic half grabens occur over much of the
northern basin (Figures 35.3, 35.7) and are inlled
by Wessel Group sediments of Basin phase 1. Theyare bounded by simple planar normal faults that have a
generally NESW strike, and dip to either the northwest
or southeast, suggesting approximately NWSE
extension. Towards the centre of the basin, a displacement
along these faults of up to 7000 m has been estimated
(Totterdell 2006). In the western part of the northern
Arafura Basin are WNWESE-oriented accommodation
zones across which the polarity of the faults switches from
northwesterly directed throw in the south to southeasterly
directed throw to the north. A series of small extensional
faults on the western margin of the basin has a NNWSSE
orientation, sub-parallel to the interpreted direction ofextension. Totterdell (2006) suggested that the orientation
of these cross faults may have been inuenced by the pre-
existing structural fabric of the underlying Pine Creek
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(northern Arafura Basin)
Arafura Basin
McArthur Basin
Money Shoal Basin
Money ShoalBasin
(Arafura Basin)
Pine Creek Orogen
Pine Creek Orogen
inferredTriassic
compressiondirection
inferredCarbPermian
extensiondirection
inferredNeoproterozoic
extensiondirection
132 133 134 135
0 50 km
IndonesiaAustralia
PalaeoMesoproterozoicbasinsPalaeoMesoproterozoicorogens
Triassic thrust fault
Late Carboniferousnormal fault
A12-183.a
i
MesozoicCenozoic
section in Figure 35.2
Goulburn Graben
Offshore Arafura Basin(under cover)
Archaean
Neoproterozoicnormal fault
A B
dry, abandoned
Petroleum exploration well
oil show
oil/gas show
oil indication
oil/gas indication
A
B
Tuatara-1
Cobra-1A
Kulka-1
Money Shoal-1 Chameleon-1
Torres-1
Tasman-1
Arafura-1
Goulburn-1
Poor seismic imaging:large, widely spaced faults
Figure 35.7. Arafura Basin fault map (compiled from Totterdell 2006, gures 19, 21). Neoproterozoic extensional faults (purple) aremapped at base of Wessel Group. Dashed red lines show accommodation zones, across which the polarity of faults switches fromnorthwesterly directed throw in south to southeasterly directed throw in north. Base Kulshill Group equivalent faults (blue) are mostlyLate Carboniferous extensional faults, many of which experienced MiddleLate Triassic reverse reactivation. Thrust fault to south ofKulka-1 formed during Triassic deformation.
Orogen. In the eastern part of the basin, there appears to
be a change in architecture to large-displacement, widely-
spaced faults. This change in structural style could reect
variations in the underlying basement fabric from west to
east, from the complex deformation and strong structural
fabric of the Pine Creek Orogen to the mildly deformed
and eastward-thickening succession of the McArthur
Basin (Totterdell 2006).
Minor Palaeozoic deformation
No known signicant deformation events occurred between
deposition of Basin phases 2 (middle CambrianEarly
Ordovician), 3 (earlymiddle Palaeozoic) and 4 (Late
CarboniferousEarly Permian). Despite the presence
of lengthy hiatuses between the Wessel, Goulburn and
Arafura groups, the Palaeozoic basin succession is
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Arafura Basin
relatively structurally conformable (Totterdell 2006).
The only indication of structural movement in the early
middle Palaeozoic succession is the absence of parts of the
Goulburn and Arafura groups in some of the wells drilled
in the Goulburn Graben, suggesting that there was some
localised uplift and erosion prior to deposition of the Arafura
Group. The timing of this minor disturbance coincides with
the Middle Devonian Pertnjara-Brewer events of the Alice
Springs Orogeny in central Australia (see Aileron Province)
and suggests it may be related to the far-eld effects of these
events. The hiatus of approximately 45 million years between
the Arafura Group and the overlying Kulshill Group correlates
with the nal, Early Carboniferous phase (Eclipse Event) of
the Alice Springs Orogeny. Although there is no seismic
evidence of any widespread contractional deformation of the
Arafura Basin at that time, there is evidence of signicant
localised uplift and erosion, with at least 1000 m of Arafura
Group missing at Tasman-1 (Totterdell 2006).
Late CarboniferousEarly Permian extensional faulting
The Goulburn Graben formed during a phase of Late
CarboniferousEarly Permian northeastsouthwest
extension. It is a narrow, highly structured zone that has
a west-northwesteast-southeast trend in the east and a
northwestsoutheast trend in the west (Figures 35.3, 35.7).
This orientation might be reecting the underlying structural
grain of basement rocks (Totterdell 2006). Along much of its
length, the Goulburn Graben has the morphology of a half
graben, with master detachment faults dening the northern
margin and the southern marginal faults only intermittently
developed. The bounding fault system to the north dips at
an angle of about 50 to the south-southwest or southwest.CarboniferousPermian extensional faulting appears to
have been conned to the Goulburn Graben, as there is
little seismic evidence for extensional faulting of this age
elsewhere (Totterdell 2006).
MidLate Triassic contraction
During the MiddleLate Triassic, the Arafura Basin, and in
particular the Goulburn Graben, experienced a major phase
of contractional deformation (Basin Phase 5 of Totterdell
2006). The effects of this deformation varied markedly across
the basin. In the Goulburn Graben, it was relatively intense
and was characterised by folding, inversion on pre-existingfaults, the formation of new thrust faults, uplift and erosion.
In the northern Arafura Basin, the affects of the deformation
were less intense; limited contractional reactivation of
Neoproterozoic half grabens resulted in the inversion of
some Neoproterozoic extensional faults and the formation of
inversion anticlines. The direction of regional compression
is interpreted to have been NNW SSE and was highly
oblique to the dominant fault trends of the Goulburn Graben,
resulting an element of dextral strike-slipor transpressional
movement on parts of the fault system (Totterdell 2006).
Minor latest Triassic/Early Jurassic extensional faulting
After the Triassic deformation event, the margins of the
Arafura Basin were uplifted, resulting in a basinward tilt,
followed by erosion and the formation of a peneplain across
the basin and adjacent basement areas. During this period
of erosion, the basin appears to have been affected by a
minor extensional episode that involved relatively small-
displacement, planar normal faulting within the upper part
of the Arafura Basin succession. On the western margin
of the basin, some older faults were reactivated and
Triassic inversion anticlines were offset (Totterdell 2006).
This faulting appears to predate the unconformity at the
base of the Money Shoal Basin and is therefore probably
older than later Jurassic extensional episodes that partly
controlled deposition of the Money Shoal Basin succession
(Struckmeyer 2006c).
MINERAL RESOURCES
The offshore Arafura Basin is very prospective for
petroleum, but to date, there have been no commercial
hydrocarbon discoveries. In the onshore Arafura Basin,
known mineral occurrences include bauxite on Marchinbar
and Elcho islands, and a small iron ore occurrence nearGaliwinku (Figure 35.5). The following summary of these
occurrences is derived from Ferenczi (2001).
Bauxite
Lateritic bauxite has developed on Neoproterozoic rocks of
the Wessel Group at Marchinbar and Elcho islands.
Marchinbar Island
Bauxite deposits were rst reported from Marchinbar
Island ( ) by Owen (1949), after he receivedsamples, collected by the Northern Territory Coastal
Patrol Service, that assayed up to 40.8% Av.Al2O
3. The
main lateritic bauxite deposits lie on the east coast of the
island and were investigated by the Australian Aluminium
Commission in the early 1950s. Ore resources for the seven
tested deposits total 9.94 Mt and average 46.0% available
Al2O
3and 4.0% reactive SiO
2(Owen 1953).
The deposits are developed over sedimentary rocks
of the Marchinbar Sandstone. The bauxite ore consists
predominately of cemented pisoliths of gibbsite, that have
light brown and red-brown cores (Owen 1954). A tubular
bauxite bed underlies pisolitic ore in several of the deposits
(eg Able, Sphinx Head, Dog and Easy). Tubular ore reaches amaximum thickness of about 2 m and lenses out to the west,
where the westerly deposits are all pisolitic (Ferenczi 2001).
The underlying laterite is up to 10 m thick and largely consists
of nodular ferricrete. The largest known deposit on the island
is Able, which occupies an area of about 880 000 m2. One
hundred and forty-two sampling pits were excavated by the
Australian Aluminium Commission on a 61 x 122 m grid.
A non-JORC Resource is given at 4.7 Mt at 47.1% Al2O
3
(Ferenczi 2001). Ore thickness varies from 0.76 m (cut-off) to
5 m and averages 2.4 m (Owen 1953). Pisolitic bauxite forms
the bulk of the resource (97%); the remaining 3% consists of
massive and tubular bauxite, which underlies the pisolitic orein the eastern section of the deposit. Bauxite quality usually
varies with depth and lower grades are often found in the
upper and lower portions of the prole. The upper 0.51 m
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of the bauxite bed in the eastern area of the deposit contains
1025% quartz sand and ne detrital material. Dry screening
of samples from this area gave an average recovery factor of
96% silica is in the form of free quartz (1.1%) and reactive
(mostly kaolinite) silica (3.0%). Iron oxides (Fe2O
3), which
are mainly in the form of goethite, average 15.7% and TiO2
averages 3.3% (Ferenczi 2001).
Elcho Island
At the eastern side of Elcho Island, two bauxite occurrences,
separated by about 3 km, were recorded by Plumb (1965).
These occurrences consist of thin loose intervals of pisolitic
and tubular bauxite that unconformably overlie unaltered
Marchinbar Sandstone (Plumb and Gostin 1973). The
pisolitic layer is about 2 m thick and forms a series of
discontinuous exposures over a 3 km strike length. Sand
dunes cover the bauxite, adjacent to and away from the
coast. A single sample from one of the occurrences assayed
45.7% Al2O
3and 25% SiO
2(Plumb 1965). The high silica
value may indicate contamination by quartz grains derived
from nearby sand dunes. A laterite sample obtained during
reconnaissance work by BHP (1964) near the southernmost
occurrence assayed 25.7% Al2O
3, 28.0% total SiO
2 and
23.3% Fe2O
3. This area is essentially untested and may host
bauxite deposits comparable to those on Marchinbar Island
(Ferenczi 2001).
Iron ore
Elcho Island iron ore deposit
The Elcho Island iron ore deposit is a bauxitic lateriticprole developed within the Elcho Island Formation. The
deposit extends for about 2.5 km along the western coastline
of the island, just to the north of Galiwinku. A lower sandy
haematite layer and an upper haematitic sandstone bed are
present in the upper part of the laterite prole. The massive
lower haematite bed is up to 0.45 m thick and contains the
bulk of the iron ore resource (600 000 t grading 60.4% Fe
and 0.054% P), as estimated by Rix (1964b). Most of the ore
lies at or near the surface, with the overburden gradually
increasing to the north where it reaches a maximum of 6 m.
The overlying haematitic sandstone is up to 1.2 m thick and
averages 40.4% Fe and 0.57% P (Rix 1964b).
Petroleum
The Arafura Basin is considered to have signicant potential
for petroleum, but so far there have been no commercial
discoveries. Oil shows and in situoccurrences of bitumen
are known from a number of stratigraphic levels. Nine
exploration wells have been drilled, all within the Goulburn
Graben, and four of these have recorded signicant oil
shows in Palaeozoic strata. The majority of the basin outside
the Goulburn Graben remains underexplored.
In the early 1920s, bitumen was reported from Elcho
Island, leading to the formation of the Elcho Island Naphthaand Petroleum Company, which drilled several unsuccessful
holes in the 1920s on Elcho Island (Bell 1923). In the 1960s
and early 1970s, stratigraphic drilling was carried out on
Bathurst and Melville islands (McLennan et al 1990). In
1971, Shell Development (Australia) Pty Ltd drilled the
rst well in the offshore Arafura Basin (Money Shoal-1) to
test the Mesozoic Money Shoal Basin succession. At about
the same time, Elf Aquitaine Petroleum was operating in
the central southern region of the Arafura Sea. These two
operators carried out extensive mapping based on seismic
data and dened the Goulburn Graben as an important
structural feature. The next phase of exploration in the early1980s involved a number of operators, including Diamond
Shamrock Corporation, Esso Australia Pty Ltd, Petrona
Exploration Australia SA and Sion Resources Ltd. A
3
3
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150 km
MarchinbarIsland
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0
13630'1100'
1300'
1200'
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lands
Arnhem Land
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Bauxite deposit
Sand dunes
Laterite
Marchinbar Sandstone
Raiwalla Shale
Strike and dip of strata
Arafura Sea
A12-194.ai
. Geology and location of bauxite deposits on MarchinbarIsland (after Ferenczi 2001, modied from Plumb 1965).
Geology and mineral resources of the Northern Territory
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35:14
typical TOC range is
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35:15
Arafura Basin
Barber PM, Carter PA, Fraser TH, Baillie PW and Myers K,
2004. Under-explored Palaeozoic and Mesozoic petroleum
systems of the Timor and Arafura seas, northern
Australia continental margin: in Ellis GK, Baillie PW and
Munson TJ (editors) Timor Sea Petroleum Geoscience.
Proceedings of the Timor Sea Symposium, Darwin,
Northern Territory, 1920 June 2003. Northern Territory
Geological Survey, Special Publication1.
Bell NC, 1923. Discovery of asphaltum on Point Bristowe,
Elcho Island. Northern Territory Geological Survey,
Technical Report GS1923-0001/1.
BHP, 1964. Report on geological investigations carried out
on Permit to Enter No113/1. BHP Pty Ltd. Northern
Territory Geological Survey, Open File Company Report
CR1964-0007.
Boreham CJ, 2006. Chemical maturity assessment and
oil correlation in the Arafura Basin: in Struckmeyer
HIM (compiler) New datasets for the Arafura Basin.
Geoscience Australia, Record 2006/06.
Boreham CJ and Ambrose GJ, 2007. Cambrian petroleum
systems in the southern Georgina Basin, NorthernTerritory, Australia: in Munson TJ and Ambrose GJ
(editors) Proceedings of the Central Australian Basins
Symposium (CABS), Alice Springs, Northern Territory,
1618 August, 2005. Northern Territory Geological
Survey, Special Publication 2, 254281.
Bradshaw J, Nicoll RS and Bradshaw M, 1990. The Cambrian
to PermoTriassic Arafura Basin, northern Australia.
APEA Journal30, 107127.
Brown DA, Campbell KSW and Crook KAW, 1968. The
geological evolution of Australia and New Zealand.
Pergamon Press, Oxford.
Carson LJ, Haines PW, Brakel A, Pietsch BA and Ferenczi PA,1999. Milingimbi, Northern Territory (Second Edition).
1:250 000 geological map series explanatory notes,
SD-53-02. Northern Territory Geological Survey, Darwin
and Australian Geological Survey Organisation, Canberra
(National Geoscience Mapping Accord).
Crick IH, Boreham CJ, Cook AC and Powell TG, 1988.
Petroleum geology and geochemistry of Middle
Proterozoic McArthur Basin, Northern Australia II:
assessment of source rock potential.American Association
of Petroleum Geologists, Bulletin72(12), 14951514.
Dunnet D, 1965.Arnhem Bay-Gove, Northern Territory (First
Edition). 1:250 000 geological map series explanatory
notes, SD 53-03, 04. Bureau of Mineral Resources,Australia, Canberra.
Earl KL, 2006. An audit of wells in the Arafura Basin.
Geoscience Australia, Record 2006/02.
Edwards DS, Summons RE, Kennard JM, Nicoll RS,
Bradshaw J, Bradshaw M, Foster CB, OBrien GW and
Zumberge JE, 1997. Geochemical characteristics of
Palaeozoic petroleum systems in Northwestern Australia.
APPEA Journal37(1), 351379.
Ferenczi PA, 2001. Iron ore, manganese and bauxite deposits
of the Northern Territory.Northern Territory Geological
Survey Report 13.
Fortey RA and Cocks LRM, 1986. Marginal faunal beltsand their structural implications, with examples from the
Lower Palaeozoic. Journal of the Geological Society of
London143, 151160.
Geoscience Australia, 2008. Arafura Basin. http://www.
ga.gov.au/oceans/rpg_Arafura.jsp.
Geoscience Australia, 2012. Petroleum geological summary,
release areas NT12-1 and NT12-2, Money Shoal Basin
and Arafura Basin, Northern Territory. Australia 2012.
Offshore petroleum exploration acreage release. http://
www.petroleum-acreage.gov.au/release-areas/
documents/arafura/Money%20Shoal_Release.pdf.
Haines PW, 1998. The carbonaceous fossilChuaria Walcott
(Neoproterozoic) from the lower Wessel Group, Arafura
Basin, northern Australia.Alcheringa 22, 18.
Helby R, 2006. A palynological reconnaissance of new
cuttings samples from the Arafura-1, Kulka-1 and
Tasman-1 wells: in Struckmeyer HIM (compiler) New
datasets for the Arafura Basin. Geoscience Australia,
Record 2006/06.
Higgins KL, 2009. Petroleum prospectivity of the northern
Australian region. Geoscience Australia, Record2009/04.
Jackson MJ, Sweet IP and Powell TG, 1988. Studies on
petroleum geology and geochemistry, Middle Proterozoic
McArthur Basin, Northern Australia I: petroleumpotential.APEA Journal28(1), 283302.
Laurie JR, 2006a. Middle Cambrian fauna from the
Jigaimara Formation, Arafura Basin, Northern Territory:
in Struckmeyer HIM (compiler) New datasets for the
Arafura Basin. Geoscience Australia, Record2006/06.
Laurie JR, 2006b. Macrofossils from Petrona Arafura 1,
Goulburn Graben, Arafura Basin.Geoscience Australia,
Professional Opinion2006/01.
Laurie JR, 2006c. Early Middle Cambrian trilobites from
Pacic Oil and Gas Baldwin 1 well, southern Georgina
Basin, Northern Territory.Memoirs of the Association of
Australasian Palaeontologists 32, 127204.McDougall I, Dunn PR, Compston W, Webb AW, Richard JR
and Bonger VM, 1965. Isotope age determinations of
Precambrian Rocks of the Carpentaria region, Northern
Territory.Journal of the Geological Society of Australia
12, 6790.
McLennan JM, Rasidi JS, Holmes RL and Smith GC, 1990.
The geology and petroleum potential of the western
Arafura Sea.APEA Journal30, 91106.
Moore A, Bradshaw J and Edwards D, 1996. Geohistory
modelling of hydrocarbon migration and trap formation
in the Arafura Sea. PESA Journal24, 3551.
Moss S, 2001. Extending Australian geology into eastern
Indonesia and potential source rocks of the IndonesianArafura Sea. PESA News49, 5456.
Nicoll RS, 2006a. Cambrian and Ordovician sediments and
biostratigraphy of the Arafura Basin, offshore Northern
Territory, Australia: in Struckmeyer HIM (compiler)
New datasets for the Arafura Basin. Geoscience
Australia, Record2006/06.
Nicoll RS, 2006b. Devonian stratigraphy and biostratigraphy
of the Arafura Basin, offshore Northern Territory,
Australia: in Struckmeyer HIM (compiler) New datasets
for the Arafura Basin. Geoscience Australia, Record
2006/06.
Nicoll RS and Bladon GM, 1991. Silurian and LateCarboniferous conodonts from the Charles Louis Range
and central Birds Head, Irian Jaya, Indonesia. BMR
Journal of Australian Geology & Geophysics 12, 279286.
Geology and mineral resources of the Northern Territory
Special publication 5
-
8/12/2019 GNT_Ch35_Arafura.pdf
17/17
Arafura Basin
Nicoll RS, Shergold JH, Laur ie JR and Bischoff GCO,
1996. Cambrian and Ordovician biostratigraphy of the
Arafura Basin, Northern Australia. Geological Society
of Australia, Abstracts41, 318.
Owen HB, 1949. Examination of a supposed bauxite-
bear ing area on Cobourg Peninsula, NT. Bureau of
Mineral Resources, Australia, Record 1949/041.
Owen HB, 1953. Bauxite in the Wessel Islands, Arnhem
Land, NT. Bureau of Mineral Resources, Australia,
Record 1953/039.
Owen HB, 1954. Bauxite in Australia.Bureau of Mineral
Resources, Australia, Bulletin 24.
Petroconsultants, 1989. Arafura Basin. Northern
Territory Geological Survey, Petroleum Basin Study.
Petroconsultants Australasia Pty Ltd.
Pietsch BA, Rawlings DJ, Creaser PM, Kruse PD,
Ahmad M, Ferenczi PA and Findhammer TLR, 1991.
Bauhinia Downs, Northern Territory (Second Edition).
1:250 000 geological map series explanatory notes,
SE 53-03. Northern Territory Geological Survey,
Darwin.Plumb KA, 1963. Explanatory notes on the Wessel
Islands-Truant Island 1:250,000 geological series sheet
SC53-15/16. Bureau of Mineral Resources, Australia,
Record1963/134.
Plumb KA, 1965. Wessel Islands-Truant Island, Northern
Territory (First Edition). 1:250 000 geological map
series explanatory notes, SC 53-15, 16. Bureau of
Mineral Resources, Australia.
Plumb KA and Gostin VA, 1973. Origin of Australian
bauxite deposits. Bureau of Mineral Resources,
Australia, Record 1973/156.
Plumb KA and Roberts HG, 1992. The geology ofArnhem Land, Northern Territory. Mineral Provinces
15. Bureau of Mineral Resources, Australia, Record
1992/55.
Plumb KA, Shergold JH and Stefanski MZ, 1976.
Signicance of Middle Cambrian trilobites from Elcho
Island, Northern Territory.BMR Journal of Australian
Geology and Geophysics1, 5155.
Price PL, 1997. Permian to Jurassic palynost ratigraphic
nomenclature of the Bowen and Surat Basins: in Green
PM (editor) The Surat and Bowen Basins, South-east
Queensland Queensland Minerals and Energy Review
Series. Queensland Department of Mines and Energy,
Brisbane, 137178.Purcell R, 2006. Palynology report Arafura-1, Goulburn-1
and Tasman-1, Goulburn Graben, Northern Territory,
Australia: in Struckmeyer HIM (compiler) New
datasets for the Arafura Basin. Geoscience Australia,
Record2006/06.
Rawlings DJ, Haines PW, Madigan TLA, Pietsch BA,
Sweet IP, Plumb KA and Krassay AA, 1997. Arnhem
Bay-Gove, Northern Territory (Second Edition).
1:250000 geological map series explanatory
notes, SD53-03, 04. Northern Territory Geological
Survey, Darwin and Australian Geological Survey
Organisation, Canberra (National Geoscience MappingAccord).
Rix P, 1964a. Junction Bay Northern Territory (First
Edition). 1:250 000 geological map series explanatory
notes, SC 53-14.Bureau of Mineral Resources, Australia,
Canberra.
Rix P, 1964b. Iron ore deposits, Elcho Island, Northern
Territory. Bureau of Mineral Resources, Australia,
Record, 1964/022, 210.
Rix P, 1965.Milingimbi, Northern Territory (First Edition).
1:250 000 geological map series explanatory notes,
SD-53-02. Bureau of Mineral Resources, Australia,
Canberra.
Shergold JH, Southgate PN and Cook PJ, 1988. Middle
Cambrian phosphogenetic system in Australia. Bureau
of Mineral Resources, Australia, Record 1988/42, 7881.
Sherwood N, Russell N and Faiz M, 2006. Thermal
maturity evaluation using a combination of FAMM and
conventional organic petrological analyses for samples
from a suite of wells in the Arafura Basin, Australia:
in Struckmeyer HIM (compiler) New datasets for the
Arafura Basin. Geoscience Australia, Record2006/06.
Southgate PN and Shergold JH, 1991. Application ofsequence stratigraphic concepts to Middle Cambrian
phosphogenesis, Georgina Basin, Australia.BMR Journal
of Australian Geology and Geophysics 12, 119144.
Struckmeyer HIM (compiler), 2006a.New datasets for the
Arafura Basin. Geoscience Australia, Record 2006/06.
Struckmeyer HIM (compiler), 2006b. Petroleum geology
of the Arafura and Money Shoal basins. Geoscience
Australia Record 2006/22.
Struckmeyer HIM, 2006c. Basin evolution: Money Shoal
Basin: in Struckmeyer HIM (compiler) Petroleum
geology of the Arafura and Money Shoal basins.
Geoscience Australia Record 2006/22, 2937.Struckmeyer HIM, 2006d. Potential play types and evidence
for hydrocarbons: in Struckmeyer HIM (compiler)
Petroleum geology of the Arafura and Money Shoal
basins. Geoscience Australia Record 2006/22, 5560.
Struckmeyer HIM and Earl KL, 2006a. Introduction: in
Struckmeyer HIM (compiler) Petroleum geology of the
Arafura and Money Shoal basins. Geoscience Australia
Record 2006/22, 13.
Struckmeyer HIM and Earl KL, 2006b. Petroleum systems
elements: in Struckmeyer HIM (compiler) Petroleum
geology of the Arafura and Money Shoal basins.
Geoscience Australia Record 2006/22, 3845.
Struckmeyer HIM, Ryan GJ and Deighton I, 2006.Geohistory models for Arafura Basin wells and pseudo-
wells: in Struckmeyer HIM (compiler) New datasets
for the Arafura Basin. Geoscience Australia, Record
2006/06.
Totterdell JM, 2006. Basin evolution: Arafura Basin: in
Struckmeyer HIM (compiler) Petroleum geology of the
Arafura and Money Shoal basins. Geoscience Australia,
Record2006/22, 428.
Zhen Yongyi, Laurie JR and Nicoll RS, 2011. Cambrian
and Ordovician stratigraphy and biostratigraphy of the
Arafura Basin, offshore Northern Territory. Memoirs
of the Association of Australasian Palaeontologists 42,437457.