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Transcript of Gorter Et Al APPEA 2009 Permian West Australia
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APPEA Journal 20093
THE PERMIANTRIASSIC BOUNDARY
IN WEST AUSTRALIA:
EVIDENCE FROM THE BONAPARTE
AND NORTHERN PERTH BASINS
EXPLORATION IMPLICATIONS
Lead author
John
Gorter
the presence of reworked sediments and paleontologic
material (both conodonts and spore-pollen) and to th
significance of geochemical shifts.
The age of the basal Kockatea Shale (northern Per
Basin) and the basal Mt Goodwin Sub-group (Bonapar
Basin) is reassessed using palaeontological data, au
mented by carbon isotopic measurements and geochem
cal analyses, supported by wireline log correlations an
seismic profiles. The stratigraphy of the latest Permia
to Early Triassic succession in the Bonaparte Basin also revised, as is the nomenclature for the Early Triass
Arranoo Member of the Kockatea Shale in the norther
Perth Basin. The Mt Goodwin Sub-group (new rank)
composed of the latest Permian Penguin Formation ove
lain by the Early Triassic Mairmull, Ascalon and Fishbu
formations (all new).
KEYWORDS
Permian-Triassic boundary, western Australia, northerPerth and Bonaparte basins, palaeontology, carbon istopes, well log correlations, 2D and 3D seismic, redefine
Mt Goodwin Sub-group and Penguin Formation, defineMairmull, Ascalon, Fishburn formations (new), ArranoMember, tectonics, eustacy, source rocks.
INTRODUCTION
The Early Triassic sedimentary succession is one of thmost tightly age-controlled intervals in the Phanerozosedimentary record. Recent advances in the radio-isotopmethods of dating of ashfall tuff zircons are producinreproducible results with error bar constraints of +/- 0Ma (Mundil et al, 2001; 2004; Mattinson, 2005; Galfetet al, 2008). In China a biostratigraphically (ammonoiand conodonts) well-constrained succession from the LaPermian (Changhsingian) through to the Middle Anisiaand containing literally hundreds of interbedded tuhorizons has been examined (Galfetti et al, 2008). Tab1 shows the revision of the age constraints in the EarTriassic from GTS 2004 (Gradstein et al, 2004) throughpreliminary revision by Ogg et al (2008) to the most rececompilation of Galfetti et al (2008). The time constrainon this Early Triassic interval demonstrate that the durtion of the Griesbachian Substage was only about 0.49 Mthe Dienerian about 0.53 Ma, the Smithian about 0.73 Mand the Spathian about 2.87 Ma. The short duration
J.D. Gorter1, R.S. Nicoll2, I. Metcalfe3, R.J. Willink4
and D. Ferdinando5
1Eni Australia40 Kings Park RoadWest Perth WA 60052Geoscience Australia
GPO Box 378Canberra ACT 26013
University of New EnglandSchool of Environmental and Rural ScienceEarth Studies Building C02
Armidale NSW 23514Origin Energy339 Coronation DriveMilton QLD 40645Murphy Australia OilLondon House, Level 1216 St Georges TerracePerth WA 6000
[email protected]@[email protected]@originenergy.com.au
ABSTRACT
Several sedimentary basins in west Australia contain
petroleum reservoirs of Late Permian or older age that
are overlain by thick shaly sequences (4002,000 m) that
have been assigned an Early Triassic age. The age of the
base of the Triassic shales has been, and continues to be,
contentious with strata being variously ascribed to the
latest Permian (Changhsingian Stage) or wholly within
the earliest Triassic (Induan Stage). In the Perth Basin
the Permian-Triassic boundary appears to be located
somewhere in the Hovea Member of the Kockatea Shale.
In the Bonaparte Basin, the boundary would appear to
be either in the uppermost Penguin Formation or at the
boundary between the Penguin and Mairmull formations.
The uncertainty of the boundary placement relates
to the interpretation of the sedimentological, biostrati-
graphic and geochemical record in individual sections and
basins. Major problems relate to the recognition, or even
the presence of unconformities, complications related to
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312APPEA Journal 2009
J.D. Gorter, R.S. Nicoll, I. Metcalfe, R.J. Willink and D. Ferdinando
these time intervals may well contribute to our inabilityto recognise sediments of the early part of this interval insome regions of the Western Australia margin.
Marine Triassic rocks are widespread in the Bonaparte,Browse, Canning, northern Carnarvon and Perth basins(Fig. 1). Many petroleum exploration wells have penetrat-ed Triassic strata and together with widespread seismicprofiling in the search for oil and gas resources, enable arobust lithostratigraphy to be established. The Early Tri-
assic sedimentary succession is predominantly composedof marine fine-grained clastic sediments and occasionalinterbedded carbonates, with total thickness ranging from4002,000 m, deposited over a time interval of 5.1 millionyears (Ogg et al, 2008). Most of the Early Triassic formationsidentified in the literature are based on lithostratigraphy,that is, correlated by electric log profiles and dominantrock types, with some biostratigraphy included by way ofpalynology. Unfortunately, most of the Australian Triassicspore-pollen zones are endemic to the region (Balme, 1969;1990; Balme and Foster, 1996; Dolby and Balme, 1976;Helby et al, 1987) and correlations to better-dated strata
elsewhere in the world is somewhat problematic. In someinstances, particularly in the upper part of the Triassic,dinoflagellates can be correlated outside of the Australianregion (e.g. Balme, 1969; 1990; Balme and Foster, 1996),and in even fewer instances conodonts and ammonoidsprove useful in correlation (e.g. Nicoll and Foster, 1998;Nicoll, 2002; Skwarko and Kummel, 1974).
In the Perth Basin, the basal Triassic shales are seals tounderlying Permian reservoirs (e.g. Cliff Head and Hoveafields) and also interpreted to be source rocks (Thomasand Barber, 2004), and minor oil and gas reservoirs arepresent in the regressive Early Triassic strata at the Don-gara oil and gas field (Arranoo Member). In the Bonaparte
Basin the basal Triassic shales form the ultimate seal forPermian reservoirs at the Prometheus, Rubicon, Fishburn,Petrel and Tern fields and include thin reservoir qualityand gas-bearing sandstones at Blacktip1 and Ascalon1A(Ascalon Formation, see below).
The primary correlation is by wireline log curve match-ing between petroleum exploration wells, supported byconodont and palynological control in shallow marine tocontinental strata. Inter basinal correlations are made us-ing the same methodology but more emphasis is placed onthe matching of chronostratigraphic surfaces supportedby the generally short-lived conodont faunas. In addition,carbon isotope profiles over the Permian-Triassic transitionprovide information on the base of the Triassic System
by means of correlation to well-dated extra-Australianmeasured sections controlled by detailed palaeontology(Galfetti et al, 2008; Mundil et al, 2001, 2003).
STRATIGRAPHIC NOMENCLATURE AND THETRIASSIC/PERMIAN BOUNDARY
Bonaparte Basin
The present lithostratigraphic nomenclature of Triassicrocks known from the subsurface across the Timor Sea, and
Table 1. Radiometric ages in million of years (Ma) of the base of Early Triassic Substages from different studies.
xmas0027.dgnScotese (2000)
60
30
0
30
60
Warm Temperate
Arid
Arid
Arid
Tropical
Perth Basin
Carnarvon BasinWarmTemperate
Bonaparte Basin
Figure 1. Locality and palaeogeographic map for the Early Triassicshowing continental distributions and inferred temperature regimes
(after Scotese, http://www.scotese.com/lpermcli.htm) and the
position of the Perth, Carnarvon and Bonaparte basins.
Stage Substage Gradstein et al (2004) Ogg et al (2008)
Anisian
Basal age 245+/-0.15 247.4
Spathian
Olenekian 248.1 249.6
Smithian
Basal age 249.7+/-0.7 251
Dienerian
Induan 250.3 251.5
Griesbachian
Basal age 251+/0.4 252.5
Permian
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APPEA Journal 20093
The Permian-Triassic boundary in west Australia: evidence from the Bonaparte and Northern Perth basinsexploration implicatio
outcrops in the southeastern Bonaparte Basin (Dickins etal, 1972; Mory, 1988, 1991), is illustrated in Figure 2. Cor-relation between wells relied on wireline log similarities.
The basal Triassic unit redefined by Mory (1988) wasthe Mt Goodwin Formation of the Kinmore Group, recog-nised regionally as a seismically bland package from thesoutheastern part of the Bonaparte Basin (e.g. Petrel field),
westwards across the Londonderry High (e.g. Osprey1area) and onto the Ashmore Platform (e.g. Sahul Shoals1area). The Mt Goodwin Formation was originally definedby Helby (1974) from Petrel1 well between 2,887 and3,464 m, where it consists of a series of interbedded shalesand siltstone with minor fine-grained sandstones.
Defining the base of the TriassicBonaparteBasin
The base of the Triassic in the Bonaparte Basin has gen-erally been considered to be at the base of the Mt GoodwinFormation (now Sub-group); however, in some wells there
is a shaly section similar to the Mt Goodwin Sub-groupbetween the undoubtedly Late Permian Tern Formationand the well-dated basal Triassic. This unit was called thePenguin Formation by Gorter (1998). Log correlations inthe southern Bonaparte Basin (e.g. Fig. 3) show that thereis an unconformable contact between Late Permian andEarly Triassic strata in the region of Fishburn1 and thisunconformable relationship is supported by seismic pro-files and is well illustrated by 3D seismic at Blacktip1,where well-defined dendritic systems are incised into thetop of the Tern Formation (Fig. 4). The two Permian lime-stones sequences seen in Petrel2 in Figure 3 are readily
correlated on seismic profiles across the Bonaparte Basand the erosion of the Late Permian Dombey Limestoneevident at Fishburn1. In this well there is a shaly intervbetween the eroded top of the Cape Hay Formation anthe base of the dated Mairmull Formation (new nameThis shaly sequence is assigned to the Penguin Formatioand contains theP. microcorpusOppel Zone at Fishburn
(Fig. 5). The major change in the carbon isotopic profileseen to occur at the base of theP. microcorpusOppel Zonin Fishburn1, but the most negative values lie at the baof theL. pellucidusOppel Zone (Fig. 5).
If the top of the Permian is defined as lying betweetheL. pellucidusOppelZone and theP. microcorpusOppeZone, then the most likely positioning of the basal Triassis at the lightest carbon isotopic horizon, i.e. the top of thPenguin Formation. The base of the Penguin Formationa clearly defined unconformity with the Tern Formatioand Dombey Formations absent by erosion. The base of thPenguin Formation was cored in Tern5. In the core thbase of the Penguin Formation lies below a granite pebb
lag described from about 2,545.2 m in the core above thTern Formation (Fig. 6). Palynological information frojust above the pebble lag indicated the lowerP. microcorpOppel Zone is present in a nearshore depositional enviroment (Purcell, 2008). The granite pebble horizon suggeslong distance transport from granitic terrain to the sout
The major isotopic break in Tern3 (data from Morant1996) also occurs below the base of the P. microcorpOppel Zone (Fig. 7). The isotopic shift in Tern3 is satoothed in pattern, with more negative isotopic valuincreasing up section (Fig. 7). Helby (1983, in the Ternwell completion report) placed the base of the Triassic
3247.dgn
Early Triassic
Anisian
Ladinian
S7
S6
S5
S4
S3
S2
S1
PollardFm
OspreyFm
CraneForm
ation
Anjo Sst Mbr
Ascalon FmFishburn Fm
Mairmull Fm
Penguin Fm
? ?
? ?
Ol1,2,3
In2In1
Lad3
Lad2Lad1
An4
An3
An2
UnnamedUnnamed
N. aldae
C. timorensis
N. pakistaniensis
S. ottii
S. quadrifidus
T. playfordii
K. saeptatusN. dieneri
Sandstone
ShaleLimestone
240
250
260
Epoch / StageTethyan
sequencesPalynology Sequences
Age(Ma) (Hardenbol
et al. 1998)
Baseconodont
zone(after Ogg & Nicoll,
in press)
Micro-plankton
Spores /pollen
(Mory, 1988)
West EasHigh Low
(Haq et al.1987)
CurrentStratigraphy Stratigraphy
West East
Timor Sea
Permian
(Changhsingian)
Longterm
Carnarvonsequences
(Gorter, 1994)
Whimbrel Sst Mbr CapeLondonde
rry
Fm
Osprey
MtGoodwin
Sub-group
Tern Fm
and older
Londonderr
y
Fm
Mt GoodwinFm
Figure 2.Stratigraphy of the Timor Sea region and Bonaparte Basin (modified from Gorter, 2008 unpublished poster).
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J.D. Gorter, R.S. Nicoll, I. Metcalfe, R.J. Willink and D. Ferdinando
12600'
12800'
Perth
W.A.
N.T.
S.A.
QLD
VIC. T
AS.
N.S.W.
TIMOR
S
EA
Fishburn1
Tern3
0.0
0.1
0.2
0.6
-35
-30
-20
0
200
3500
3000
4000
500
Cores
100
Permian
1750
2000
2500
3000
2250
2750
Petrel2
0.0
0.8
L.pel
luc
idus
0.7
Jurassic
TopPearce
TopTorrens
CapeHay
0.4
0.3
0.5
-25
2900
2800
2700
2600
3400
3300
3200
3100
3900
3800
3700
3600
4100
4200
4300
0.1
0.30.40.5
0.2
0.6
Top
of
Cores
Triassic
Cores1-3
10Cores1-9
GR
DT(sec/m)
Palynology
T.
playfordii
K.
saeptatus
K.
saeptatus
Wey
landites
D.
stel
lata
TopPearc
eFormation
TopMtGo
odwin
Sub-group
CapeLondonderry
Depth
(m)
2500
5
8
9
"
@3192m
Depth
(m)
-35
-30
-20
-25
2100
2000
1900
1800
1700
1600
2200
2300
2400
2500
2600
Depth
(m)
0.0
0.1
0.2
0.6
-35
-30
-20
0.4
0.3
0.5
-25
?
Caved
TopFossilHead
PenguinFormation
Typesectionof
FishburnFormation
Typesectionof
MairmullFormation
LimestoneMarkers
EarliestTriassicisotopictrend
Transitionisotopictrend
LatestPermianisotopictrend
P.
samoi
lov
ich
ii
P.
microcorpus
upper
Stage5
c
upper
Stage5
b
l
ower
Stage
5b
l
ower
Stage
4
C.
torosa
upper
Stage5
a
Stage3
b
3
8
13
"
@2580m
L.pel
lucidus
OspreyFo
rmation
FishburnFormation
AscalonF
ormation
MairmullF
ormation
PenguinF
ormation
13
11
Carbon
Isotopes
0
200
500
Cores
100
GR
DT(sec/m)
Palynology
Carbon
Isotopes
0
200
500
Cores
100
GR
DT(sec/m)
Palynology
Carbon
Isotopes
TernForm
ation
TopDomb
eyFormation
CapeHay
Formation
TopTorrens/FossilHead
Formation
s
3363.dgn
Fishburn1
NB:Logsandgeochemical
datafromPetrel-2adjusted
downtocorrelatewith
Petrel-4corebased
palynologyandcarbon
isotopicvalues.
Datum:baseAscalonFormation
69.5km
65.1km
Petrel2 P
P5
.5
-
PP6
PP6
PP5
.4
-
PP6
PP5
.4
PP4
.3
.2
PP4
.3
.2
-
PP5
Approx
.
PP5-P
P6
i
nT
ern-4
Tern3
up
P.
microcorpus
l
o
P.
microcorpus
Approx
.
P.
microcorpus
i
nT
ern-3
Figure3.CorrelationsectionbetweenFishburn1,Tern3andPetrel2acrossthePermian-Triassictransition.NotetheunconformablecontactatFishburn1isalsosupportedby
theseismicandwelllogcorrelationtooffsetwells,withtheDombeyandTernformationsbotherodedatthewellsite.
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APPEA Journal 20093
The Permian-Triassic boundary in west Australia: evidence from the Bonaparte and Northern Perth basinsexploration implicatio
the base of the upperP. microcorpus Oppel Zone (Fig. 8).Detailed examination of the Permian-Triassic transition inTern3 shows a sharp boundary between the Tern Forma-tion and the overlying Penguin Formation indicated by thegamma ray (GR) curve (Fig. 8). Also shown in Figure 8 arethe palynofacies percentages of opaque organic matter,plant debris and acritarchs (after Helby, 1983, in Tern3well completion report). It is clear that over the transitioninterval marked by theP. microcorpusOppel Zone that thedecreasing amount of opaque organic debris parallels theupward negative shift of the carbon isotopic curve (Fig.8). Note that the carbon isotopic values were derived from
digitising a figure from Morante (1996) whereas the othercurves are derived from digital data in the Tern3 wellcompletion report; there may be a slight discrepancy indepth between these measurements.
In Petrel4 the boundary is not so clearly demarcatedbecause the isotopic break occurs above the 9 casing(data from Morante, 1996), with the cuttings-based isotopicvalues below the casing shoe having heavier isotopic values.These cuttings-derived values are not as isotopically heavyas from the cored Cape Hay Formation section below theDombey Formation limestone marker (with the notableexception of the sample from 3,600 m where over 93.5%
of the kerogen is from acanthomorph acritarchs) (Fig. 9The evidence from the southern Bonaparte Basin show
that the major unconformity lies between theP. microcorpOppel Zone and older Late Permian strata. The uncoformity is supported by 2D and 3D seismic data, well locorrelations and palynology. The carbon isotopic profilshow a negative inflexion at the base of the Penguin Fomation above relatively monotonous heavy isotopic valuthrough the Permian (except where complicated by venegative measurements equated to marine incursions). Thbase of the Triassic is marked by the most negative carboisotope values and the incoming of theL. pellucidusZon
Northern Perth Basin
The basal Triassic stratigraphic subdivisions of the PerBasin were established by Playford et al (1976) and thsummary published by Cockbain (1990) is essentially uchanged by subsequent publications, other than the reognition of the Hovea Member at the base of the KockatShale (Thomas and Barber, 2004) and the reinterpretatiothat at least some of the sandstone bodieslike the Dongra Sandstoneare of Late Permian age. Nonetheless, theis considerable debate about the nature of the Permia
Fig04.dgn
Dendriticpatterns
Dendriticpatterns
Top TernFormation
Blacktip1
0 4km
Figure 4. Dendritic channel-like feature near the top of the Tern Formation or base of the Penguin Formation near Blacktip1. Smal
channel forms are seen to the southeast of the well (note the major linear features shown in red are faults).
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J.D. Gorter, R.S. Nicoll, I. Metcalfe, R.J. Willink and D. Ferdinando
Triassic transition (Fig. 10) and the precise placement ofthe boundary. Thomas and Barber (2004) contended thatdeposition was essentially continuous across the Permian-Triassic boundary and Metcalfe et al (2008) suggestedthat the lack of Early Triassic (Induan) conodont faunasfrom any locality in Western Australia probably indicatesa depositional break in the boundary interval.
In establishing the Hovea Member of the KockateaShale, Thomas and Barber (2004) extended the base ofthe Kockatea Shale into the Late Permian. They placedthe base of the Kockatea Shale into the upper part of theWuchiapingian Stage and included both theD. parvitholatoP. microcorpusOppel Zones in the Permian. There maybe some question regarding the recognition of theD. parvi-tholaOppel Zone in the base of the Hovea Member, but theinterpretation of aP. microcorpusOppel Zone in the baseof the Hovea Member is more certain (Thomas et al, 2004).
The Arranoo Member is the interbedded fine-grainedsandstone and siltstone facies in the upper Kockatea Shalein onshore wells in the Dongara gas field area (Gilchristand Holloway, 1983; Mory and Iasky, 1996: Crostella andBackhouse, 2000), and is overlain by a regressive unit, theWoodada Formation (Mory and Iasky, 1996). The ArranooMember contains theK. saeptatusOppel Zone.
Kockatea Shale
The Kockatea Shale crops out in the northernmost PerthBasin around the Northampton Complex and as far north as
2300
2500
2700
-30 -25
2100
1900
1800
3076.dgn
Hyland BaySub-group
Mt GoodwinSub-group
MetersMD
GR (API)
0 200 500 100 Palynology
(Morante 1996)
marine
marine
marine
Cuttings based
Jurassic
1900
2000
2100
2200
2300
2400
2500
2600
2700
2800
C.torosa
P.samoilovichii
L.pellucidus
P.microcorpus
upperStage5c
upperStage5b
upperStage5a
lowerStage5b
lowerStage4
Stage3b
Fishburn Formation
Ascalon Formation
Mairmull Formation
Penguin Formation
Cape Hay Formation
Torrens Formation
Fossil Head Formation
Pearce Formation
DT (sec/m)
2550
GR (API)
0 200
0 200
2540
2539
2550
2551
Digitised GR (API) Core
2542
2544
2546
2548
2552
2554
2542
2544
2546
2548
LogDepth
(m)
CoreDepth
(m)
2541
2543
2545
2547
2549
Penguin
Formation
Granite pebble lag
Shelly lag
Tern5
Tern
Formation
LowerP. microcorpus
LowerP. microcorpus
Fig06-3400.dgn
Figure 5. Carbon isotopic profile across the Permian-Triassic transition in Fishburn1 (isotopic data digitised from Morante, 1996).
Figure 6.Correlation of cores from Tern5 by means of a gamma ray
log of the cores to the downhole gamma ray logs (data from Tern5
well completion report, Santos, 1998a, b). The core description is
by N.M. Lemon in the completion report. Palynological dating by
Purcell (2008).
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The Permian-Triassic boundary in west Australia: evidence from the Bonaparte and Northern Perth basinsexploration implicatio
2350
2550
-30 -25 -20-35
3077.d
Mt Goodwi
Sub-group
Hyland BaySub-group
MetersMD
GR (API)
0 200 500 100
Palynology
(Helby WCR)
Cuttings-based
(Morante, 1996)
Dombey Formation
2100
2200
2300
2400
2500
2600
K.saeptatus
L.pellucidus
Weylandites
D.stellata
upperP.microcorpuslower P.microcorpus
Fishburn Formation
Ascalon Formation
Mairmull Formation
Penguin Formation
Tern Formation
Cape Hay Formation
DT (sec/m)
Figure 7. Carbon isotopic profile across the Permian-Triassic transition in Tern3 (isotopic data digitised from Morante, 1996). Note t
maximum negative shift at the base of the Mairmull Formation below the P. microcorpusOppel Zone (based on core data).
2350
2550
Depth(m)
3086.dgn
Palynofacies( Helby, WCR )
100
150
200
0 50 -3
5
-30
-25
-20
0
2400
2450
2500
Palynology( Helby, WCR )
Carbon Isotopes( Morante, 1996 )
90
10
20
30
40
50
60
70
80
L. pellucidus
Weylandites
K. saeptatus
GR(API)
% opaques
% plant debris
% acritrachs
-?
T R I A S S I C
L A T E P E R M I A N
A
B
DOMBEY FM
CAPE HAY FM
TERN FM
MAIRMULL
FM
PENGUIN
FM
upper P. microcorpus
lower P. microcorpus
Figure 8. Details of the Permian-Triassic transition in Tern3, showing the sharp boundary between the Tern Formation and the overlyi
Penguin Formation (left hand column), the carbon isotopic profile (after Morante, 1996), and the palynology in the right hand column (fro
Helby, 1983, in Tern3 well completion report). Also shown are palynofacies percentages of opaque organic matter, plant debris and acritarc
(after Helby, 1983, in Tern3 well completion report).
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J.D. Gorter, R.S. Nicoll, I. Metcalfe, R.J. Willink and D. Ferdinando
3300
3500
3700
-30 -25
3078.dgn
Mt GoodwinSub-group
Hyland BaySub-group
MetersMD
GR (API)
0 200 500 100
Palynology
(Foster et al. 1997)
Top Pearce
Cuttings and
core-based
marine
(Morante 1996)
K.saeptatus
Coresfrom3563.6m
3100
3200
3300
3400
3500
3600
3700
3800
3900
PP5.5 -PP6
PP6
PP5.4 -PP6
PP5.4
PP4.3.2 -PP5
PP4.3.2
Approx.PP5-PP6
inTern-4
DST 4
958"casing958"
casing
Ascalon Formation
Mairmull Formation
Penguin Formation
Tern Formation
Dombey Formation
Cape Hay Formation
Fishburn Formation
DT (sec/m)
Approx. P.microcorpus
inTern-3
Figure 9. Carbon isotopic profile across the Permian-Triassic transition in Petrel4 (isotopic data from Morante, 1996; Foster et al, 1997)
indicating no marked negative shift at the base of the Penguin Formation in this well, possibly because of complications resulting from the
placement of the 9 casing. Note the highly negative marine spike in the Permian section caused by the abundance of spinose acritarchs
and the marked negative isotope excursion at the base of the Mairmull Formation.
3249.dgn
S8
S7
S6
S5
S4
S3S2
S1
? ?
Kockatea
Shale
? ?
? ? ?
Ol1,2,3
In2
Car3
Car2
Car1
In1
Lad3
Lad2Lad1
An4
An3
An2
Unnamed
Unnamed
N. aldae
C. timorensis
N. pakistaniensis
P. polygnathiformis
S. ottii
S. quadrifidus
T. playfordii
K. saeptatusN. dieneri
Early Triassic
Anisian
Ladinian
Carnian
240
250
260
Epoch / StageTethyan
sequencesPalynology Sequences
Age(Ma) (Hardenbol
et al. 1998)
Baseconodont
zone(after Ogg & Nicoll,
in press)
Micro-plankton
Spores /pollen West EastHigh Low
(Haq et al.1987)
CurrentStratigraphy Stratigraphy
West East
Perth / Abrolhos (GSWA Report 75)
Permian(Changhsingian)
Longterm
Carnarvonsequences
(Gorter, 1994)
Sandstone
Limestone
KockateaFacies
Beekeeper /Dongara
KockateaShale
(Condensedsection)
ArranooMember
Unnamed Lst marker
LesueurFormation
LesueurFormation
Woodada Formation WoodadaFormation
BookaraSandstone
WittecarraSandstone
Indoonmember/
ArranooMember
Hovea Sapropelicinterval
Hovea Inertinitic intervaland older Permian
Figure 10. Stratigraphy of the northern Perth Basin (from Gorter et al, 2008).
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Kalbarri in the southern Carnarvon Basin (Mory and Iasky,1996). Ammonoids indicate that the base of the KockateaShale in the subsurface in BMR Beagle Ridge10 is EarlyTriassic (Griesbachian), and Smithian at the top (Dickinsand McTavish, 1963; Balme, 1990; Gorter et al, 1995; Fosteret al, 1997). North of Beagle Ridge10, at Mt Minchin, ammo-noids from the lower part of the formation are of Smithian(late Early Triassic) age demonstrating that the Kockatea
Shale is time transgressive onto the Northampton Block(Playford et al, 1976). Outcrop in the north of the basin isgenerally sparse and weathered, and detailed measuredsections are non existentthe type section is 12 m thickaccording to Mory and Iasky (1996)so that well logs anddrill cuttings are the major source of lithostratigraphicand biostratigraphic information.
The Kockatea Shale is the only Triassic formation in thenorthern Perth Basin with established ties to internationalbiostratigraphy including conodonts and ammonoids, butmost of the non-marine Triassic in the basin relies on longranging spores and pollens for age dating. The KockateaShale contains the K. saeptatusOppel Zone, sometimes
sub-divided into theP. samoilovichii zone and the basalL.pellucidus zone. Conodonts from the basal limestone areusually dated as Smithian by theN. dieneri-N. pakistanensiszones. Carbon isotopic profiles have been established forthe Permian-Triassic transition in Woodada2 (Gorter etal, 1995; Foster et al, 1997), several Dongara area wells(Andrew et al, 1999; Morante et al, 1999), and Hovea3(Thomas and Barber, 2004; Thomas et al, 2004). Moranteet al (1994) and Morante (1996) provided some additionalinformation on BMR Beagle Ridge10A, but unfortunatelyinsufficient to enable a vertical profile to be drawn.
The Dongara oil and gas field is the largest hydrocar-bon pool in the northern Perth Basin. Reservoirs includeseveral named Permian sandstones that are sealed, andsourced by the overlying Early Triassic Kockatea Shale. AtDongara1 the basal part of the Kockatea Shale includes aninertinitic interval overlain by a sapropel-rich unit calledthe Hovea Member (Thomas et al, 2004). The exact age ofthe inertinitic unit is still in dispute (see above) but thesapropelic interval in the upper part of the Hovea Memberis clearly near-basal Triassic in age as it contains distinc-tive bivalves, conodonts and ammonoids that are of thesame age as well-dated Early Triassic sections elsewherein Gondwana. The sapropelic interval and the overlyingKockatea Shale proper contain theK. saeptatusOppel Zone(Fig. 11). The informally named limestone marker, whichoverlies the sapropelic unit, dated by the occurrence in
several wells of theN. pakistanensisconodont fauna (e.g.Corybas1 in Metcalfe et al, 2008), is included in the HoveaMember by Thomas et al (2004).
Defining the base of the TriassicPerth Basin
Detailed palaeontological and organic geochemical in-formation derived from cores from Dongara4 is illustratedin Figure 12. The Rock-Eval T
max, hydrogen index (HI) and
production index (PI) measurements are from in-house Enidata measured by Geotech (West, 2000). The GR (API) and
sonic (DT) logs are from digitised electric log data frothe Western Australian Department of Mines and Petrleum website. The SC GR (API) is a gamma ray log ruover slabbed core by CoreLab in 1998 for British-Borne(now Eni). The ranges of the various fossils in the corare from Dr Peter Jones (Australian National Universitpers. comm., for the ostracod Carinaknightina discarinataRSN (new conodont identifications), and McTavish (197
for the N. dieneri zone conodonts. The identification Claraia sp was by Dr Mac Dickins (deceased, ex Bureaof Mineral Resources, pers. comm.) and JDG (in houidentifications). The position of the limestone marker derived from the sonic log correlation to nearby wells ancuttings described from the Dongara4 mud log. Cores wematched to the down hole logs via the core gamma log fcores 1 to 3, and are matched at the top of core 4 based othe reported rounded pebble lag (Backhouse, 1996) anthe gamma ray curve. The interpreted trends for the latePermian (blue box) and Early Triassic (pink box) carboisotopes follows the Hovea3 data (Thomas and Barbe2004; Thomas et al, 2004) as shown in Figure 11.
The Dongara4 Rock-Eval data derived from the coresection (cores 1 to 3) show the contained organic mattis immature (also shown by vitrinite reflectivity values
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The very fine-grained sandstones of the informallynamed Indoon member in Indoon1 (Fig. 14) can be cor-related from Indoon1 to East Lake Logue1 and into someof the Woodada gas field wells, but sandstones are absentin other field wells like Woodada2, where the stratigraphicequivalent may be represented by calcareous shales de-posited on the pre-existing, pre-Triassic topographic high(e.g. Gorter and Davies, 1999, fig. 13). In the Dongara areathe Indoon member may merge with the Arranoo Member(both occur in a section containing theK. saeptatusOppelZone), but further work is required to validate this.
DISCUSSIONGorter (1994) interpreted regressive-transgressive
events in the Triassic strata of the offshore CarnarvonBasin (Fig. 1) by correlating palynological zones with thesea level curve of Haq et al (1988). These transgressiveand regressive events are correlated to sea level eventsdeduced for the Triassic succession in Tethys as determinedby Hardenbol et al (1998) in Figure 2. The Induan 1 and 2sea level events are here equated with a sea level fall atthe base of the Ascalon Formation (new name) betweensequences 1 and 2 of Gorter (1994), and the sea level fall
between sequences 2 and 3 is correlated with the Olen-kian 3 event of Hardenbol et al (1998). In the Early andMiddle Triassic, Ogg (in Gradstein et al, 2004) noted majorregressions in the Induan (In1), middle Olenkian (Ol1) andnear the top of the Olenkian (Ol4) and the late Ladinian(Lad3). In Ogg et al (2008) this was changed to limit themajor regressions to the Late Permian (late Changhsingian(end Perm)), the late Olenekian (Ol4) and the late Ladin-ian (Lad 3). The Ol4 event of Ogg et al (2008) probablycoincides with the Olenekian 3 event of Hardenbol et al(1998), but given the widespread nature of the regressiveevent at the base Ascalon Formation in the Bonaparte
Basin, probably reflected in the incoming of the Indoonmember in the northern Perth Basin, it is surprising thatit is not recognised by Ogg et al (2008). In Ogg et al (2008)peak transgressive events are shown to have occurred inthe mid to late Olenkian (Neospathodus pingdingshanensisZone) and at about the AnisianLadinian boundary level(topNevadites secedensisZone).
Isotope stratigraphy
High-resolution carbon isotope measurements frommany stratigraphic sections in south China have demon-
420
430
440
450
460
0 100
200
300
400
500
600
700
800
900
1000
0.0
0.1
0.3
0.4
0.5
1965
1970
1975
1980
1985
1990
1995
Depth(m)
Tmax HI PI
-32
-30
-28
-26
-24
-22
3073.dgn
13! C Kerogen
0.2
0 200
D.pa
rvithola
P.
microcorpus
K.saeptatus
CORE GR (API) GR (API)
in situ
Evidence ofmigrated or
hydrocarbons.
Inertinitic
Sapropelic
DONGARASANDSTONE
from Rock-Evalbasic data
Unconformity ?
maxT possiblyeffected byhydrocarbons:Temperaturevalues too low.
digitised fromThomas et al.(2004, fig. 2)
Figure 11. Rock-Eval pyrolysis digital data from Hovea3 plotted against Rock-Eval pyrolysis measurements digitised from Thomas et al
(2004, fig. 2). The overlay of the original hydrogen index (HI) values in red diamonds by the digitised values of the HI (green diamonds) from
Thomas et al (2004, fig. 2) demonstrates that the digitised 13C values for kerogen is on depth; however, the unpublished production index
data (PI) show that the section with lower isotopic values contain either in situ generated or migrated hydrocarbons, suggesting the Rock-
Eval Tmax
values reported are probably too lowthe probable break in maturity of the contained kerogen at about 1,981 m (dashed line)
could indicate an unconformity.
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The Permian-Triassic boundary in west Australia: evidence from the Bonaparte and Northern Perth basinsexploration implicatio
strated that the pronounced carbon isotopic excursion atthe Permian-Triassic boundary is not an isolated event butmerely the first in a series of large fluctuations that contin-ued throughout the Early Triassic before ending abruptlyearly in the Middle Triassic. Composite carbon isotopiccurves (13C
carb) for the well-dated Meishan locality and
other sites in China (e.g. Krull et al, 2004, fig. 8; Payne andKump, 2007; Galfetti et al, 2007, 2008), show that the light-est carbon isotopic content (i.e. the most negative values)occurs in bed 25 at Meishan in the upper Changsingian.In marine sections, such as at Meishan, the negative car-bon isotopic excursion and the Permian-Triassic boundarymay be separated by a few centimetres whereas in non-marine sections several tens or even hundreds of metresmay separate these events, and the boundary can not beplaced with any certainty within the transitional palyno-flora or vertebrate fauna (Metcalfe et al, in press). ThePermian-Triassic boundary in the Bonaparte and northernPerth basins lies within a siliciclastic-dominated succes-sion that, on the present palaeontological dating, appearto have been deposited rather rapidlyconsistent with
a stretched carbon isotopic profile (e.g. in FishburnFig. 5 and Tern3, Fig. 7). The abrupt break in the carboisotopic curve shown by Hovea3 (Fig. 11) is consistewith extremely rapid sedimentation over the inertinitand sapropelic interval boundary or a sedimentary hiatu
Payne and Kump (2007, fig. 1), demonstrated that least four marked swings in isotopic values occur in thEarly Triassic in the Great Bank of the Nanpanjiang Bas(e.g. Lehrmann et al, 2003), an isolated Permo-Triasscarbonate build-up at Guizhou in southern China (Fi15). Ogg et al (2008) have shown preliminary revised stagand substage boundary ages (our Table 1) and these havbeen further revised by Galfetti et al (2008) and used redraft Figure 15 contrasting carbon isotopic curves froGuizhou (Payne and Kump, 2007) and Guangxi (Galfetet al, 2007). Galfetti et al (2007, fig. 2) indicate the monegative isotopic excursion in the Early to Middle Triassoccurs in the early Smithian at the base of theFlemingitrursiradiatusbeds in the Jinya/Waili composite measuresection in northwestern Guangxi in southern China, aproximately equivalent to theN. dieneri-N. waageni co
420
430
440
450
460
0 100
200
300
400
500
600
700
800
900
1000
0.0
0.1
0.2
0.3
0.4
0.6
Tmax HI PI
-35
-30
-20
0.5
-25
0 200GR (API)SC GR (API)
1670
1660
1680
1690
1700
Depth(m)
1650
3074.dgn
10000.1
13! C Kerogen
Cores
Pal
ynol
ogy
K.saeptatus
P.
sinuosus
or
younger
Limestonemarker
Core1
Core2
C3
Lost
core
Barren/Permian
Roundedpebblelag
? reworkedPermian
Claraia
C. discarinataLatest Permianisotopic trend
Earliest Triassiisotopic trend
N. dienerizone
DT (sec/m)
C4
Figure 12.Dongara4 Rock-Eval Tmax, hydrogen index (HI) and production index (PI) from in house data by Geotech (West, 2000). G
(API) and DT logs are from digitised data in DoIR website fi les. SC GR (API) is a gamma ray log run over slabbed core by CoreLab in 1998 f
British-Borneo (now Eni). The ranges of the various fossils in the core are after Peter Jones (pers. comm., for the Carinaknightina discarinat
Robert Nicoll (pers. comm.) and McTavish (1973) for the N. dieneri zone conodonts; Claraiasp from Mac Dickins (pers. comm.) and Gort
(in house); and the limestone marker from sonic log correlation to nearby wells and cuttings described in the Dongara4 mud log. Cor
are matched to the down hole logs via the core gamma log for cores 1 to 3, and are matched at the top of core 4 based on the reporte
rounded pebble lag (Backhouse, 1996) and the gamma ray curve. The carbon isotopic compositions are from Morante (1996) and Moranet al (1999). The trends for the latest Permian (blue box) and Early Triassic (pink box) carbon isotopes follows Hovea3 data (Thomas a
Barber, 2004; Thomas et al, 2004) as shown in Figure 11.
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Claraia
C.
discarinata
Megaspores
MO
NDARRA
DONGARA
MT
HORNER
Co
rybas1
Dongara4
Hovea3/ST1
HOVEA
0
200
0.0
0.1
0.2
0.3
0.4
0.6
0.5
-35
-30
-20
-25
GR
100
Palynology
500
1965
1970
1975
1980
1985
1990
1995
1960
K.
saeptatus
P.
microcorpus
D.
parvithola
x=-13
Depth
(m)
Conodonts
0.0
0.1
0.2
0.3
0.4
0.6
-35
-30
-20
0.5
-25
Core1 Core2 C3
Lost
core
Cores
Roun
ded
pebbl
e
l
ag
Barren/
Perm
i
an
K.
saeptatus
1670
1660
1680
1690
1700
1650
LatestPermian
isotopictrend
EarliestTriassic
isotopictrend
Limestone
Marker
Isotopesfro
m
Morante(?)
Depth
(m)
0
200
GR
100
DT(sec/m)
Palynology
500
C4
Limestone
marker
Datum
0.0
0.1
0.2
0.3
0.4
0.6
-35
-30
-20
0.5
-25
Clarkinasp
.
C.
jolfensis
N.
dieneri
3332.dgn
Conodonts
Depth
(m)
0
200
GR
100
DT(sec/
m)
500
2220
2210
2230
2240
2250
2270
2260
2280
2200
WESTER
N
AU
ST
RAL
IA
Per
th
2915'
11500'
CoreGammahas
beenshiftedtothe
lefttohighlight
comparison
Carbon
Iso
topes
Carbon
Isotopes
Carbon
Isotopes
CORE
GR
CO
RE
G
R
Dongara4
?
Corybas1
12.5
km
7.5
km
Hovea
3/ST1
Evidenceof
migratedor
insitu
hydrocarbons.
DT(
sec/m)
P.
sinuosus
or
younger
N.
dienerizone
N.
pakistanensis
Figure1
3.Wirelinelogcorrelatio
nbetweenHovea3/ST1,Dongara4and
Corybas1acrossthePermian-Triassicboundary.Thiscorrelationindicatesthat
theHovea3boundary
islikelytobeerosionalandtheon
lapoftheTriassicovertheHovea3areaoccurredlaterthanatDongara4andCorybas1.
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odont zones (composite 13Ccarb
curve reproduced in Fig.15). Foster et al (1997) had earlier demonstrated that thecarbon isotopic content of kerogen in the Triassic couldbe artificially heavy because of the reworking of Permianwoody material with heavy isotopic values. In this isolatedbank, influx of recycled Permian wood is unlikely and theisotopic swings must be caused by other means, perhapssea level fluctuations (see Haq et al (1988) and Hardenbolet al (1998) for eustatic variations in the Early Triassic),or the episodic and catastrophic release of methane fromhydrates (e.g. Hesselbo et al, 2000; de Wit et al, 2002;Retallack and Krull, 2006).
Australian carbon isotopic curves from 13Corg
overthe Late Permian to Early Triassic transition (based ondata from Morante, 1995, etc.) have been published byMorante et al (1994) and Morante (1996) for Tern3, Foster
at al. (1997) for Petrel4, and Morante (1996) and Retalack and Krull (2006) for Fishburn1 (see Fig. 5). Whicarbon isotopic curves based on the carbon isotope valufrom organic-derived carbon (total organic componen13C
org
) are not strictly comparable to carbon isotopvalues derived from carbonate minerals (13C
carb) (e
Kump and Arthur, 1999; Retallack and Krull, 2006, fig. Arthur, 2008), as both presumably reflect the isotopic composition of the global atmosphere, it is assumed that thnegative-positive shifts in both measures move in tandemas shown by de Wit et al (2002) across the palynologicaldefined Permian-Triassic boundary from five basins the interior of the former Gondwana Supercontinent. addition, as pointed out by Giddings and Wallace (200913C
carb values derived from basinal carbonate faci
are generally lighter than proximal facies with chang
800
900
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
2000
2200
T.playfordii
Probably Permian
Kockatea Shale
Early Triassic toLatestPermian
DT (sec/m)1400 200
GR (API)
40
K.saeptatus
Palynology(Balme,
Ingram, WCR)
Jurassic
LondonderryEquivalent
OspreyEquivalent
Arranoo
Microfossils(Ingram, WCR)
50%
100%
Acritarchs
"mangroves"
Lycopods
Lycopods
Conifers
Preferre
dcorre
latio
n
Eneabba
7" @
2109m
3093.
3300
3500
3700
- 30 - 25
Alternativecorrelation
Conodonts inBeekeeper1APP4.2 to APP5age range
AratrisporitesSp
p.
Densoisporitesn
ejburgi
Triplexisporitesplayfordi
Falcisporitesaus
tralis
2100
2200
-3 0 -25 - 20-35
WoodadaFormation
Lesueur
Formation
BeekeeperFormation
CarynginiaFormation
~2400 km
INDOON1 PETREL4
2000
2100
2200
2300
2400
2500
2600
2700
2800
2900
3000
3100
3200
3300
3400
3500
3600
3700
3800
3900
Meters
MD
GR (API)
0 200 500 100 Microfossils
Cape Hay
Plover
Top Triassic
Datum :
Palynology
(Foster et al. 1997)
PP5.5 -PP6
PP6
PP5.4 -PP6
PP5.4
PP4.3.2 -PP5
PP4.3.2
Top Hyland BaySub-Group
Top Dombey
Top Pearce
Cores from 3563.6m
Base Ascalon
Ascalon Formation
Top Mt GoodwinSub-group
OspreyFormatio
FishburnFormatio
MairmullFormatio
KB = 25m, WD = 95m, TD = 3975m
Elf Aquitaine, 1988
TroughtoGroup
Cape LondonderryType Section2471-2887min Petrel-1
?
Approx.PP5-PP6inTern-4
589 "
@
3417m
Possiblefault
589 "
@
846m
DST 4
Reduviasporonites?
(Morante 1996)
S N
MD
Meters
Carbon isotopicdata in house.
Cuttings show well bottomedin Pearce limestone
Malita FormationType Section2229-2471min Petrel-1
Penguin Formatio
DT (sec/m)
Approx. T.playfordiiinPetrel-1
Approx. K.saeptatus
inPetrel-1
Approx. P.microcorpusinTern-3
Approx.P.arcoensisinPetrel-2
'Indoonmember'
Figure 14. Shallowing event (Indoon member) in the Kockatea Shale at Indoon1 recognised from the gamma ray and sonic log profi
and by a decrease in the spinose acritarch content of the palynofacies (from Indoon1 well completion report). The correlation betwe
Indoon1 in the northern Perth Basin and Petrel4 in the southeastern Bonaparte Basin shows close similarities in formation architectu
supported by palynological information and carbon isotopic measurements across the Permian-Triassic boundary.
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of 811 in age equivalent facies. Similar gradients canoccur in proximal siliciclastic facies, where much of thecontained organic matter may be derived from land plantsresulting in heavier carbon isotopic values, compared todistal settings where the organic matter is more likely tohave been derived from marine organisms, with lighterisotopic values.
The Early Triassic Kockatea Shale in the northern Perth
Basin has a distinctive log facies and contains theK. saep-tatus Oppel Zone. The last appearance of the species K.saeptatusis at the top of theB. buurensis-S. millericonodontzone, i.e. it is no younger than topmost Smithian (Ogg and
Nicoll, 2007) in the Arctic. The lower part of the formationcontains theN. dieneritoN. pakistanensisconodonts in andbelow a limy interval (i.e. the limestone marker) seen inmost northern Perth Basin wells. The overlap of conodontranges reported from Corybas1 by Metcalfe et al (2008)indicates an early Smithian age for this carbonate interval.Both species have their last appearance near the top of theB. buurensis-S. millericonodont zone, i.e. latest Smithian.
These early Smithian limestones lie below a slightlysandy interval, seen in the Indoon1 and Woodada fieldwells, in theK. saeptatus Oppel Zone that is interpretedto be the equivalent of the Ascalon Formation in the
-2 -1 0 1 2 3 4 5 6 7 8
252.5
247.88
251.48
dieneri
Stabilis
ation
MiddleTriassic
EarlyTria
ssic
Anisian
Smithian
Spathian
Age(Ma)
252.01
Gries-
bachian
250.75
-2 -1 0 1 2 3 4 5
waageni-milleri?
Dien-
erian
3082.dgn
13C
PTBexcursion
Changsin
gian
Late
Permian
Time scale from Galfetti et al. (2008) 13C
Figure 15. Composite carbon isotopic (13C) compositional changes measured across the Permian-Triassic boundary in an isolated
deep marine carbonate bank at Guizhou in southern China (after Payne and Krump, 2007, fig. 1) should be relatively free from reworked
terrestrial input which may bias the isotopic measurements. Also shown for comparison is the composite carbon isotopic (13Ccarb
) curve
from northwestern Guangxi (Galfetti et al, 2007). Both curves are fitted to the Galfetti et al (2008) timescale at the substage boundaries.
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Timor Sea wells (e.g. Fig. 14). In Fishburn1, the AscalonFormation, while itself not analysed for carbon isotopiccomposition, appears to be part of a continuum of carbonisotopic values. Values are initially increasingly negative,then switch upward through the Mairmull Formation toincreasingly positive values below the Ascalon Formation(Fig. 5). Above the Ascalon Formation in the FishburnFormation (new name), the isotopic values again become
increasingly negative upwards through the formation tobe the lightest values in the well, immediately below theunconformity at the base of the Jurassic. If the entiresedimentary section across the Permo-Triassic boundaryis present in the Bonaparte Basin wells shown in Figure 3,and assuming the sampling interval is narrow enough torecord all possible perturbations in carbon isotopic values,the lightest carbon isotopic value can be correlated withbed 25 at Meishan, and is located in the latest Permian, orat a younger light isotopic inflexion, for example near theGriesbachian-Dienerian boundary. If the former correla-tion is correct, the incoming ofL. pellucidusoccurs in thelatest Permian, or if the latter in the latest Griesbachian
or earliest Dienerian (cf. Figs 5 and 15).
Unconformities
The most negative carbon isotope values equate to thelower part of the Kockatea Shale in the northern PerthBasin and the lowermost Mairmull Formation or topmostpart of the preserved Fishburn Formation in the BonaparteBasin (Fig. 16a). The sharp break to the negative at about1,981 m in the Hovea3 core is of a comparable magnitude.The lack of any slope between the negative Smithian val-ues and the positive Permian values suggest that sectionis missing in the cored section at Hovea3 and is entirely
consistent with the Late Permian age of the P. microcor-pusOppel Zone in the positive isotopic interval, and thehighly negative isotopic part of the K. saeptatusOppelZone interval. Similar conclusions can be drawn from acomparison of the carbon isotopic curves and palynologybetween Hovea3 and Tern3 (Fig. 16b).
Support for absence of the earliest Triassic in westernAustralian basins is forthcoming from the fossil record:there are no unequivocally Griesbachian conodonts, am-monites or shelly fossils known from any basin on thewestern Australian margin. This is not to say that olderTriassic strata may not be present in undrilled basinalareas. The oldest Triassic rocks on the western Australianmargin, based on isotopic curve matching, are most likely
in the Bonaparte Basin where the latest GriesbachianP.microcorpusOppel Zone occurs in the Penguin Formation,which from well log correlations (Fig. 3) and seismic datais unconformable on the Tern Formation. Furthermore, inTern5 the base of the Penguin Formation with the lowerP.microcorpusOppel Zone (Purcell, 2008) is a granite pebblelag overlying the Tern Formation (Fig. 6). In the Blacktip1region, 3D seismic data indicates channelling of the topof the Tern Formation (Fig. 17). In the Perth Basin, thereis no conclusive evidence from dipmeter or seismic datafor an erosional break between the sapropelic and inerti-
nitic intervals of the Hovea Member in either Hovea3 Corybas1, but in other wells such as Cliff Head4, theis a clearly defined unconformity between the sapropelinterval and the older Permian based on palynology (Pucell, 2006). In this well the contact is shale-on-shale anthere is no obvious evidence of the unconformity such facies change, weathering, angularity or lag, but there a colour change and a marked palynological break (Ear
Triassic over Artinskian). A similar shale-on-shale contawith no discernible evidence of hiatus apart from palnology change and a negative carbon isotopic excursiooccurs in Woodada2 (Gorter et al, 1995; Foster et al, 1997
From a comparison of the isotopic curves (e.g. Paynand Kump (2007) and Galfetti et al (2007) in Fig. 16), can be argued that the base of the Kockatea Shale (iabove theP. microcorpusOppel Zone) is no older than laest Griesbachian and there is a substantial time gap the order of a million yearswith or without significaerosionbetween the inertinitic interval of the HoveMember and the sapropelic interval at the base of thKockatea Shale. This is clearly demonstrated at Dongara
(Fig. 12) where the unconformity occurs between the saropelic lowermost Kockatea Shale (upper Hovea Membof Thomas et al, 2004, fig. 2) and the underlying inertinitpart of the Hovea Member (Fig. 11).
Throughout the Bonaparte Basin, the base of the AscaloFormation demonstrates a widespread downward shift facies probably coinciding with the Induan 1/2 lowstan(Fig. 2). The sandy lithofacies in the proximal parts of thBonaparte Basin shales out distally until there is very littsandstone present in the system. The Indoon and Arranmembers in the northern Perth Basin may be a similacoeval lowstand deposit.
Depositional rates and palaeoclimateIn passing, the new constraints on the ages of the low
shaly units of the earliest Triassic suggests that the seeral hundred metres of the Mt Goodwin Sub-group wedeposited in basin depocentres in as little as 11.5 millioyears (averaged from Table 1), during which time there walso a marine regression and regional erosion at the baof the Ascalon Formation. This implies a depositional raof ~>500 m/million years for depocentres where seisminformation suggests up to 2 km of Mt Goodwin Sub-grouaccumulation (after compaction)a phenomenal depsitional rate for what is essentially a shallow marine paralic siltstone unitand implies a vast supply of fin
grained detritus in the hinterland that was transported inthe shallow sea. There are no known fossil river systemof basal Triassic or latest Permian age in the hinterlanof the Bonaparte Basin that may have distributed thweathered material, leaving open the possibility that mucof the finer detritus was dispersed by wind. Possibly thweathered detritus was from far afield, for example froa later Permian cool temperature desert that was locateon the craton away from the preserved Late Permian mrine strata (e.g. the Hyland Bay Sub-group contains cowater limestones and was, in the Bonaparte Basin area
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2250
2350
2200
-32
-30
-28
-26
-24
-22
GR CarbonIsotopes
100
150
200
0 50
Palynology
L. pellucidus
upperStage 5c
P. microcorpus
Depth
(m)
Unconformity ?
-32
-30
-28
-26
-24
-22
COREGR CarbonIsotopes
1970
1980
1990
1995
1985
1975
1965Palynology
K. saeptatus
P. microcorpus
D. parvithola
100
150
200
0 50
Depth
(m)
2300
Possible correlation
based on carbonisotopic valuesand palynology
Earliest Triassicisotopic trend
Latest Permianisotopic trend
Unconformity ?
-32
-30
-28
-26
-24
-22
3156.dgn
2350
100
150
200
0 50
-35
-30
-25
-20
2450
L. pellucidus
Weylandites
K. saeptatus
TRIASSIC
A
B
MAIRMULL
FM
PENGUIN
FM
upperP. microcorpus
lowerP. microcorpus
COREGR
CarbonIsotopes
CarbonIsotopes
1970
1980
1990
1995
1985
1975
1965
TERNFM
GR Palynology
Palynology
K. saeptatus
P. microcorpus
D. parvithola
Depth
(m)
100
150
200
0 50
Depth
(m)
2400
MAIRMULL
FM
PENGUIN
FM
CAPEHAY
FM
LATEPERMIAN
TRIASSIC
Fishburn1
Hovea3
A
Hovea3
Tern3B
LATE
PERMIAN
Figure 16a and b.Comparisons between the carbon isotopic composition of kerogens in Hovea3 (data from Thomas et al, 2004) and
Fishburn1 (Fig. 16a) and Hovea3 and Tern3 (Fig. 16b) (data from Morante et al, 1994; Morante, 1996). If the carbon isotopic values are
directly comparable, the preserved P. microcorpusOppel Zone isotopic values (i.e. < -24 13C) in Hovea3 equates to the lower P. microcorpus
Oppel Zone in Tern3, supporting the suggestion that most of the P. microcorpusOppel Zone is eroded at Hovea3.
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the late Early Permian (Artinskian-Kungurian) CarynginiaFormation contain ice-rafted debris reflecting renewedsubsidence but continuing seasonally cool climates withcoarse debris ice rafted into a marine embayment. Just(2003) interpreted a cool water, shallow ramp origin for thecarbonates of the Beekeeper Formation (Fig. 14), whichcontains microfossils indicative of Wordian-Wuchiapingianage (David Haig, University of Western Australia, pers.
comm. 2009), about 254268 Ma. The overlying WaginaSandstone contains coal and so is probably of latest Perm-ian age (deposited before the earliest Triassic coal gap,Retallack and Krull, 2006), probably from the Capitanianto the Wuchiapingian. Tupper et al (1994) interpreted acool but not cold environment of deposition. Given thecircumstantial evidence for cool to cold climate aroundthe northern Perth Basin during the later Permian it wouldbe expected that a large amount of glacially derived andweathered material may have been available on the cratonto fill any nearby depocentre.
In a major review of zircon provenances, Veevers et al(2005) concluded that there was uplift along the Darling
Fault to the east of the northern Perth Basin at about255 Ma (approximately the Wuchiapingian-Changhsingianboundary), with drainage to the southeast and east awayfrom the subsiding northern Perth Basin. Thus, the inputof craton-derived material to the latest Permian strata ofthe northern Perth Basin was limitedthe Hovea Memberinertinitic interval may have been deposited at this time.With transgression in the earliest Triassic and the amelio-ration of the climate (Fig. 1), the sapropelic interval of theHovea Member was laid down in a marine environmentrelatively free of influx of weathered material from theuplifted rift shoulders.
The economic implications of depositing such a largethickness of shale in such a short period of time needsto be addressed. Note that the present measured thick-nesses of these shaly units from wells and seismic data isafter compaction and dewatering. Intuitively, this rapiddeposition should push any underlying source rocks rap-idly through the oil generation window implying that inthe depocentres at least, oil generation probably initiatedduring the Triassic possibly prior to trap formation relatedto the Middle Triassic to Early Jurassic Fitzroy Movement(Colwell and Kennard, 1996).
CONCLUSIONS
This study has shown that a combination of palaeontol-
ogy, carbon isotopic curves, wireline log correlations andseismic profiles allows inter-basinal correlation of lithofa-cies across the Permian-Triassic boundary in two basins atopposite ends of Western Australiathe Bonaparte andnorthern Perth basins.
We conclude that the main Latest Permian unconfor-mity in the Perth Basin lies above theP. microcorpusOppelZone, and in the Bonaparte Basin, the main unconformitylies below the P. microcorpus Oppel Zone, unless the P.microcorpusOppel Zone is time transgressive.
Implications from this conclusion include:
The tectonic history of the Permian-Triassic boundary
differs between the Bonaparte and northern Perth ba-sins;
The apparent correlation of the Ascalon Formation and
the Indoon member lowstand units in the lower part oftheK. saeptatus Oppel Zone implies a possible eustaticconnection between the northern Perth and Bonapartebasins; and,
The different tectonic history may partly explain thelack of an equivalent to the excellent oil and gas sourcein the sapropelic unit of the basal Kockatea Shale (up-per part of the Hovea Member) of the northern PerthBasin in the Bonaparte Basin.
ACKNOWLEDGEMENTS
We would like to thank the following colleagues for dataand/or discussion: Ric Morante, Arthur Mory (GeologicalSurvey of Western Australia), Robyn Purcell (P&R PurcellGeological Consultants), Geoff Wood (Santos), and ourreferee Roger Hocking (GSWA).
In addition, the following Eni personnel contributed tothis study: Shane McGilligan and Sandra Ball (drafting)and Kon Kostas who provided the 3D time slices.
We would like to acknowledge Eni for permission topublish (JDG) and ARC Energy for access to the northernPerth Basin well data (DF).
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APPENDIX: REVISED STRATIGRAPHIC NO-MENCLATURE
The stratigraphy of the Permo-Triassic Kinmore Group(Mory, 1988, 1991) is revised with the elevation of the MtGoodwin Formation to Sub-group rank and the recogni-tion of four subdivisionsthree newto the sub-group.
Mt Goodwin Sub-group (new)
The Mt Goodwin Formation, the upper unit of the Kin-more Group of Mory (1988) was informally sub-dividedinto the Lower and Upper units (Gorter, 1998; Gorter etal, 1998). As the Ascalon Formation is here proposed fora mappable unit in the Mt Goodwin Formation overlyingan unconformity, the unit is raised to Sub-group status inthe Kinmore Group. The Kinmore Group is thus made up
of a lower Fossil Head Formation, the middle Hyland BaySub-group and an upper Mt Goodwin Sub-group. The MtGoodwin Sub-group is composed of four units: the PenguinFormation (base), the Mairmull Formation, the AscalonFormation and the Fishburn Formation (top). The base ofthe Mt Goodwin Sub-group (i.e. the base of the PenguinFormation) is defined as an unconformity overlying olderPermian strata. The top of the Mt Goodwin Sub-group (i.e.the top of the Fishburn Formation) is an erosional surfacebelow the Osprey Formation in the eastern Bonaparte Ba-sin, and the Sahul Group in the western Bonaparte andnorthern Browse basins.
Correlations are made using wireline log signatures,palynology and limited micropalaeontology supplemented
by seismic profiles. Carbon isotopic values from Fishburn1,Petrel4 and Tern3 have been used to constrain the BaseTriassic-Top Permian contact.
Penguin Formation (additional information)
Definition and type sectionThe formation was for-mally defined by Gorter (1998) for a medium grey to darkgrey-brown claystone in Tern3 between (2,4002,449 m).
AgeThe Penguin Formation contains theP. microcorpusOppel Zone, considered by Helby et al (1987) to be latestPermian probably Changsingian.
Depositional environmentIn cores from Tern4 and 5and sidewall cores from Tern3, the finely laminated shales
contain low percentages of spinose acritarchs, particularlyin the lower part (Tern3, Fig. 5), and exhibit little, ifany, bioturbation. The lithology and palynofacies indicateoxygen-poor depositional environment. Jeff Wood (Santos,pers. com., 2007) suggested a lacustrinal facies.
Stratigraphic relationshipsUnconformably overliesthe Late Permian Hyland Bay Sub-group at Fishburn1,and appears to conformably underlie the Mairmull For-mation (Fig. 5).
Distribution and thicknessThe Penguin Formation ispresent throughout the southern Bonaparte Basin. It maybe absent at Troubadour1 and appears to be missing at
Kelp Deep1 on the Sahul Platform (Gorter and Davies,1999, fig. 5), where the Mt Goodwin Sub-group onlaps theTroubadour High.
SynonymsThe unit was previously included in the MtGoodwin Formation based on its lithological similarity.Helby (1983) in the Tern3 well completion report calledtheP. microcorpus-bearing interval the A and B shales andsuggested an affinity with the Hyland Bay Formation.
Mairmull Formation (new name)
Definition and type sectionThe Mairmull Formation,named after Mairmull Creek near the Triassic outcrop of MtGoodwin southeast of Wadeye, Northern Territory, wherethe unit unconformably overlies the Late Permian HylandBay Sub-group (of Gorter, 1998), and is unconformablebelow the Ascalon Formation (new name, see below). Theunit consists predominantly of claystone and siltstone andcoarser sediments are rare. The type section is designatedin Fishburn1 between 2,121 m and 2,320 m (Fig. 5).
AgeEarly Triassic based on its position in the
Kraeuselisporites saeptatus Oppel Zone of Dolby andBalme (1976). In the Perth Basin theK. saeptatusOppelZone is associated with theN. dieneritoN. waageniconodontzones suggesting correlation with the Dienerian to lateSmithian sub stages. The transition between the Permianand the Triassic may be marked by the largest negativeshift in carbon isotopic values as seen in Fishburn1 andTern3 (Figs 5 and 7).
Depositional environmentThe Mairmull Formationwas deposited in shallow water conditions as shown bythe occurrence ofLingulaand conchostracans in Petrel1,the presence of spinose acritarchs, and the greenish andsometimes reddish colouration of the sediment. While thegamma ray log profile is generally monotonous, in several
wells the lower beds are slightly more radioactive than theupper part of the formation, and there is a gradual increasein the proportion of thin sandstone beds in the uppermostinterval below the base of the Ascalon Formation. The car-bon isotopic profile at Fishburn1 mirrors the gamma rayprofile suggesting an initial transgressive portion of theformation shown by increasing upward negative isotopicvalues followed by a sustained upward trend to heaviercarbon isotope values (Fig. 5). While unproven in this well,the changes in the isotopic composition probably reflectthe proportion of spinose acritarchs present in the forma-tion, the larger percentage in the transgressive strata anda lessening proportion of these saline indicators in theinterpreted regressive part of the unit (e.g. see Gorter et
al, 1995; Foster et al, 1997).Stratigraphic relationshipsWhere the Penguin For-
mation is absent, the Mairmull Formation overlies uncon-formably the Late Permian Hyland Bay Sub-group. TheMairmull Formation unconformably underlies the AscalonFormation.
Distribution and thicknessThe Mairmull Formation ispresent throughout the Bonaparte Basin. It may be absentat Troubadour1 on the Sahul Platform where the Mt Good-win Sub-group onlaps the Troubadour High. The formationis recognised in Echuca Shoal1 in the eastern BrowseBasin where it is intruded or contains basaltic volcanics.
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SynonymsThe only synonym for the Mairmull Forma-tion is the Lower Mt Goodwin Formation of Gorter, 1998;Gorter et al (1998), now superseded.
Ascalon Formation (new name)
Definition and type sectionThe Ascalon Formation isa prominent, widespread, sandstone/siltstone unit roughly
located in the middle of the Early Triassic Mt GoodwinSub-group in the southern part of the Bonaparte Basin. InAscalon1A, the formation is described from cuttings asvery fine to fine-grained very well sorted sandstone, withtraces of silt and clay minerals, carbonaceous specks andpoor to fair visual and inferred intergranular porosity. Thelogs suggest the unit is tight, but a total gas show of 11.31%associated with a drilling break and the appearance ofunconsolidated or less cemented sandstone in the