GNT_Ch35_Arafura.pdf

8/12/2019 GNT_Ch35_Arafura.pdf

1/17

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.


2/17

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).

Geology and mineral resources of the Northern Territory

Special publication 5


3/17

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).




4/17

35:3

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.




5/17

Arafura Basin

35:4

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.




6/17

35:5

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.




7/17

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).


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.




8/17

35:7

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




9/17

Arafura Basin

35:8

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




10/17

35:9

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




11/17

Arafura Basin

35:10

(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




12/17

35:11

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




13/17

Arafura Basin

35:12

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

EASY

FOX

DOG

ABLE

BAKER

RED CLIFF

SPHINX HEAD

150 km

MarchinbarIsland

Gove

0

13630'1100'

1300'

1200'

Wes

selIs

lands

Arnhem Land

3

0 5 10 km

Bauxite deposit

Sand dunes

Laterite


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).




14/17


15/17

Arafura Basin

35:14

typical TOC range is


16/17

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.




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).


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).


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.

Documents

GNT_Ch35_Arafura.pdf