International Journal of Coal Geology 45 Ž2000. 55–84
www.elsevier.nlrlocaterijcoalgeo
A review of the Traralgon Formation in the Gippsland Basin —
a world class brown coal resource
Guy R. Holdgate ) , Malcolm W. Wallace, Stephen J. Gallagher, David Taylor
School of Earth Sciences, UniÕersity of Melbourne, ParkÕille, Victoria, 3010, Australia
Received 14 March 2000; accepted 21 July 2000
Abstract
The Traralgon Formation contains by far the largest brown coal resources in the Gippsland Basin, and is probably
unequalled in the World for any single basin deposit of its type. Out of an indicated resource of 345 billion tonnes ŽGt.,
approximately 10 Gt are currently listed as economically recoverable reserves. Low ash content Žave. 2.9% db. but higher
organic sulphur contents Žave. 1.72% db. largely reflect the near-coastal depositional environments under which much of the
original extensive peat swamps accumulated. The contained plant matter and coal types indicate a high-latitude rainforest
environment where rainfall and temperatures were higher than present, and where lithotype cycling occurs. The coals appear
to have accumulated at specific high stand periods of coastal onlap towards the end of the Middle and Late Eocene, and
eustatic sea-level changes play an important role in development of the coal seams. The timing for maximum coal
accumulation takes place at the apogee of a greenhouse world shortly before the cooling trends into the early Oligocene.
During this time over 100 Gt of carbon was sequestered into these coal deposits. q 2000 Elsevier Science B.V. All rights
reserved.
Keywords: Australia; Gippsland Basin; Traralgon Formation; brown coal; sequence stratigraphic analysis; palaeogeography
1. Introduction
The Gippsland Basin occupies the premier Australian position with regard to the scale and size of
its contained brown coal and petroleum energy resources. The largest Australian accumulation of Tertiary brown coal, where total in situ coal resources of
over 400.0 billion tonnes ŽGt. have been defined by
drilling, occurs within the onshore parts of the basin
ŽGloe, 1967, 1975; Holdgate, 1984; Barton et al.,
)
Corresponding author. Fax: q601-393-447761.
E-mail address: [email protected]
ŽG.R. Holdgate..
1995.. Two of the five major coal seams in the
onshore Gippsland Basin are defined within Palaeogene-aged Traralgon Formation, where individual
seam thicknesses often exceed 100.0 m. Where these
seams occur in stratigraphic superposition, they can
form a total thickness of over 150.0 m of continuous
low ash coal. The Traralgon Formation coal seams
occur over most of the onshore Gippsland Basin and
underlie both the younger Neogene-aged Morwell
and Yallourn Formation coal seams and their marine
carbonate facies equivalents of the Seaspray Group
Žincludes the Lakes Entrance Formation..
The Traralgon Formation coal seams subcrop generally beneath - 30.5 m overburden across the cen-
0009-2541r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 1 6 6 - 5 1 6 2 Ž 0 0 . 0 0 0 2 0 - 3
56
G.R. Holdgate et al.r International Journal of Coal Geology 45 (2000) 55–84
Fig. 1. Location and structural setting map of the Gippsland Basin in southeast Australia, showing the Traralgon Formation coal fields, offshore oil and gas fields, and basement
outcrops.
G.R. Holdgate et al.r International Journal of Coal Geology 45 (2000) 55–84
tral Baragwanath Anticline uplift area, where 9.6 Gt
of presently economic reserves are available ŽGloe,
1975.. However, they have no mining history. The
remainder Žca. 335 Gt. coal resource usually occurs
at depths ranging between 100.0 and 500.0 m below
ground level. The total Traralgon Formation coal
resource is more than three times larger than that of
the presently mined Neogene coals ŽFig. 1.. The
relationship between the predominantly non-marine
Traralgon Formation coal measures and their
marginal marine and marine facies equivalents in the
offshore part of the Gippsland Basin have not been
documented before. The interpretations rely on palynoflora zone equivalents, and unpublished faunal
biostratigraphic data ŽTaylor, 1986..
The specific objectives of this study are to Ž1.
summarise all the bore and well data including coal
lithotype and coal quality data, Ž2. present a regional
stratigraphic correlation of the Traralgon coal seams
and interseam sediments, Ž3. establish the interplay
between non-marine and marine environments, Ž4.
present a sequence stratigraphic analysis of the Traralgon Formation, and Ž5. produce palaeogeographic
maps for the coal measures.
2. Data sources and definitions
The regional stratigraphic interpretations rely essentially on subsurface oil well and coalrgroundwater bore core and cuttings logs, and down-hole
geophysical log interpretations carried out by the
authors. The database includes the following:
2.1. The former state electricity commission of Victoria (SECV) and Geological SurÕey of Victoria (GSV)
coal, stratigraphic, and groundwater bore database
This is the prime source for coal data in Gippsland and includes the results for over 20,000 bores.
For regional studies a selection has been made of
about 150 key andror better-sampled bores. SECV
coal cores were routinely crushed and analysed at the
SECV Herman Research Laboratories ŽHRL. for in
situ coal moisture and ash content over 3.0-m composite intervals, ash constituents over 6.0-m intervals, and proximate and ultimates over 12.0-m intervals. A series of special lithotype bores were drilled
57
and logged by the former Victorian Brown Coal
Council ŽVBCC. and SECV for coal-to-oil conversion studies. Four of these bores sampled the Traralgon Formation coals.
2.2. Oil company well data
In the onshore Gippsland Basin, approximately 25
wells are available that contain modern sets of geophysical logs Žgamma, resistivity, SP, neutron, sonic
and density. together with some sidewall coring and
cuttings sampling. For regional studies, the geophysical log traces are particularly useful. Coal quality
data is generally absent in the deeper areas of the
basin where petroleum exploration is concentrated.
However, coal rank determinations exist through vitrinite reflectance measurements in some wells. In the
offshore Gippsland Basin over 100 wells are available, all with a modern suite of geophysical logs,
cuttings and core.
2.3. Lithology definitions
The coals Žash - 10.0% dry basis. are all soft to
hard brown coals, and most would be classified
within the American ASTM classification system
ŽASTM, 1979. as falling within the Lignite B range.
In the more deeply buried areas near the coast this
rank may increase, and in the offshore part of the
basin they are in part referred to the sub-bituminous
rank ŽGeorge, 1970; Smith, 1981..
3. General stratigraphy and structure
The Gippsland Basin covers an approximate area
of 56,000 km2 ŽSmith, 1981., of which two-thirds
occurs offshore. The parts covered by this report
include ca. 16,000 km2 onshore and ca. 10,000 km2
in the immediate offshore area ŽFig. 1.. The Gippsland Basin includes a Cretaceous- to early-Tertiaryaged, mainly non-marine sedimentary sequence
formed during the Gondwanan continental breakup. The sequence Žincluding Traralgon Formation.
consists of highly mature siliciclastics deposited in
fluvial–deltaic settings, and mudstones with lesser
carbonates deposited in marginal to open marine
environments ŽFalvey, 1974; Wilcox, 1978; Abele et
al., 1988; Wilcox et al., 1992.. In the offshore basin
58
G.R. Holdgate et al.r International Journal of Coal Geology 45 (2000) 55–84
Fig. 2. Stratigraphy of the onshore Traralgon Formation coal measures. Also shown are their offshore equivalents, and their relationship to the relative coastal onlap curves,
biostratigraphy and ages ŽHaq et al., 1988..
G.R. Holdgate et al.r International Journal of Coal Geology 45 (2000) 55–84
this succession is known as the Latrobe Group,
where informal regional subdivisions have been put
forward by various authors including Bodard et al.
Ž1986. and Smith Ž1988.. In these schemes, the
Žmainly onshore. Traralgon Formation largely relates
to the Upper Latrobe Group, although the exact time
equivalence relies on palynologically defined biostratigraphic zones, e.g., Partridge Ž1976. and Brown
Ž1986.. James and Evans Ž1971. introduced new
stratigraphic names for seismically defined channel
infill successions, which are a feature of the Upper
Latrobe Group further offshore, as shown in Fig. 2.
Marshall and Partridge Ž1988. describe the channel
successions, and their palynological ages.
The Gippsland Basin succession shows a progressive westward shift in marine facies that reflects the
progressive opening of the Tasman Sea and Southern
Ocean. By Oligocene times most of the basin had
become marine in character, and carbonate marls and
limestones of the Seaspray Group Žincluding Lakes
Entrance Formation. up to 3 km thick extend to
recent times. Exceptions to this occur in the Latrobe
Valley, Baragwanath Anticline and Alberton Depression where non-marine Morwell and Yallourn
Formation coal sequences continued to accumulate
behind sand barrier systems ŽThompson, 1980;
Thompson and Walker, 1982; Holdgate, 1996..
In the onshore Gippsland Basin, Tertiary sediments were confined to the west, north and south by
uplifted basement rock terrains of the Eastern Victorian Highlands and the Wilsons Promontory–Bassian
Rise. Major uplift of the central Balook Block is
dated as Late Miocene, when uplift and stripping
exposed down to Lower Cretaceous rocks in the
Strzelecki Hills ŽBolger, 1991.. Rates of uplift decreased eastward, forming the east-plunging Baragwanath Anticline — the divide between the Latrobe
ValleyrLake Wellington Depressions, and the AlbertonrSeaspray Depressions as shown in Fig. 1. In
the deeper onshore synclines, up to 700 m of Tertiary-aged Latrobe Valley Group strata can occur.
Post-coal measure ŽLate Miocene–Pliocene. folding, uplift and erosion of the Latrobe Valley Group
and Alberton Coal Measures dominates the structural
events occurring within the onshore Gippsland Basin
ŽThomas and Baragwanath, 1949, 1951; Gloe, 1960,
1976; Bolger, 1984, 1991.. Uplift of basin margin
areas is also of prime significance, as it results in
59
minimal overburden Ž- 30.5 m. for access to the
brown coal reserves. Evidence for this erosion can be
seen in all the anticlinal structures adjacent to the
Balook Block, and along the northern and southern
basin margins ŽBolger, 1984, 1991.. Areas of maximum uplift have been largely stripped of their
Tertiary cover; this stripping may exceed 200.0 m
vertically in places, such as along the Baragwanath
Anticline and Loy Yang Dome. However, included
within the overall Baragwanath Anticline is the Gormandale Syncline where Traralgon Formation coal
measure sediments may exceed 400.0 m in thickness.
Earlier structural movements on the Rosedale MonoclinerFault appear to control the northern limit of
the lowermost Traralgon 2 coal seams, and the Morwell MonoclinerFault appears to control the westerly limit to the Traralgon 1 coal seams. Apart from
these earlier structuring events, the Palaeogene and
early Neogene in the onshore basin Žincluding Traralgon Formation. is dominated by relatively even
basin-wide subsidence.
4. Detailed stratigraphy and distribution of the
Traralgon Formation
The Traralgon Formation ŽGloe, 1960; Hocking,
1972. is dated by the Nothofagidites asperus and
Lower Proteacidites tuberculatus spore–pollen zone
ages as being of Middle Eocene to Early Oligocene
age ŽPartridge, 1971.. It is widespread throughout
the onshore Gippsland Basin, and is known to extend
offshore. The formation comprises interbedded conglomerates, sandstones, shales and coal seams;
coarser-grained sandstones and conglomerates predominate towards the base; coals and shales in the
middle; and sandstones, shales, and minor coals near
the top.
The main Traralgon Formation coalfields occur
along the Baragwanath Anticline ŽGormandale,
Willung, Holey Plains, Coolungoolun, Longford
Dome, Stradbroke, Boodyarn, and Won Wron. and
also on the Loy Yang, Gelliondale and Greenmount
Domes ŽFig. 1.. Traralgon Formation coals are also
known to occur at Alberton, where they underlie the
Alberton Coal Measures.
Thick conglomerate sequences Žup to 200.0 m.
known as the Honeysuckle Hill Gravels ŽGloe, 1975.,
underlie the coal seams at Holey Plains, Coolun-
60
G.R. Holdgate et al.r International Journal of Coal Geology 45 (2000) 55–84
X
Fig. 3. East to west cross-section ŽA–A . showing all the major Traralgon Formation coal seams and interseams. Base line projected along the floor of the T2 coal seam — the
first major coal seam.
G.R. Holdgate et al.r International Journal of Coal Geology 45 (2000) 55–84
X
Fig. 4. North to south cross-section ŽB–B . showing all the major Traralgon Formation coals seams and interseams. Base line projected along the floor of the T2 coal seam —
the first major coal seam.
61
62
G.R. Holdgate et al.r International Journal of Coal Geology 45 (2000) 55–84
goolun, and Longford Dome, and equivalent sandstone facies occur in the Seaspray Depression. Across
the Baragwanath Anticline the main coal seams
recognised are the Traralgon 1 ŽT1. and Traralgon 2
ŽT2. seams. In the Latrobe Valley Depression only
the younger T1 seam occurs north and west of the
Rosedale MonoclinerFault, where it extends a short
distance to the west of Loy Yang. The T1 seam at
Gormandale and Flynns Creek Syncline can be over
100.0 m thick, and at Stradbroke the T2 seam is also
over 100.0 m thick. Further east at Holey Plains,
Coolungoolun, and Longford Dome, thinning, splitting, and interseam erosion has reduced the T1 and
T2 seams each to about 40.0 m in thickness ŽHoldgate, 1987.. On the Baragwanath Anticline and in
the Seaspray Depression the T1 and T2 seams are
usually separated by a coarse sandstone interval,
which has regional significance. At Gormandale,
George Ž1965. recognised a T q seam that he included in the T1. This seam is now viewed as the T0
coal seam interval that is better developed in the
Lake Wellington and Seaspray Depressions.
Stratigraphic correlation of all Traralgon Formation coal seams is shown on diagrammatic cross-sections across the onshore and near-offshore Gippsland
Basin ŽFigs. 3 and 4.. The correlations are discussed
in detail under the following names: Traralgon 0
ŽT0., Traralgon 1 ŽT1., Traralgon 2 ŽT2. and Honeysuckle Hill Gravels and equivalents. We suggest the
use of a new name, the Dutson Sand Member, for
the sandy facies equivalents to the T0 and T1 coals
ŽFigs. 3 and 4., previously referred to as ‘the upper
sandy unit’ of the Traralgon Formation ŽHocking,
1976.. A large proportion of the total Traralgon
Formation coal resource lies beneath limestones and
marls of the Seaspray Group ŽLakes Entrance Formation. in the Lake Wellington and Seaspray Depressions. In the Seaspray Depression a number of seams
may aggregate up to 150.0 m of coal in places. T2
coals can also extend over 25.0 km offshore ŽHoldgate, 1984..
5. Traralgon Formation coal reserves, resources
and properties
The total measured Traralgon Formation coal reserves Žwhere overburden is less than 91.4 m, overburden to coal ratios are less than 2:1, and minimum
seam thicknesses are ) 15.0 m. amounts to nearly
10 Gt within 14 different fields Žsee Table 1 and Fig.
1.. A total coal resource for Traralgon Formation
coals in Gippsland, as estimated from the coal
isopachs Žwith a minimum seam thickness of 3.0 m.
ŽFigs. 5 and 6., and at present-day compaction, is
estimated to be 345 Gt, assuming an averaged raw
coal density of 1.1213 grcm3. Calculations for the
total carbon stored in the onshore Traralgon Formation coal seams Žnot including carbonaceous sediments. is calculated from 67% carbon Žby weight. in
dry coal ŽHiggins et al., 1980.. Assuming an average
moisture content of 50%, then total weight of carbon
in the Traralgon Formations’ 345 Gt coal resource is
33.5% of this total, or 115 Gt. This resource exceeds
the estimated Oligo–Miocene coal resources for
Gippsland by a factor of about three times. It is also
thought to be one of the largest single brown coal
deposits in the world ŽGloe, 1991.. However, the
thick limestone cover over much of the deposit
would preclude development other than at basin
margins or on the Baragwanath Anticline.
Traralgon Formation coal seams near the basin
edges have, with some exceptions, the lowest moisture contents for Gippsland Basin coals Žaverage
55%.. With deeper burial and folding, moistures
below 50% are normally found. Samples analysed
from deeper oil wells have similar ash yields to those
from shallower deposits, but are higher in rank, with
bed moisture as low as 30%. Table 2 derived from
Gloe Ž1980. gives weighted averages for the coal
properties Žmoisture, ash, volatiles, carbon, hydrogen, sulphur, and calorific value. in the main Traralgon Formation coalfields of the Latrobe Valley area.
The table uses figures quoted for coal where the
overburden is less than 30.5 m. Locations of the
main Traralgon Formation coal field areas used to
calculate the Table 2 values are shown in Fig. 1.
Irrespective of burial depth, seam moisture content
of the Traralgon Formation coals decreases with age
of the seam, reflecting the influence of geologic time
on the coalification path. On average, there is a
decrease of 2.7% in moisture content between Traralgon 1 and Traralgon 2 seams. This results in many
cases of abrupt step-like profiles in moisture content
across seam and sequence boundaries.
The ash yield of Latrobe Valley type brown coals
is expressed on a dry coal basis, and is broadly
G.R. Holdgate et al.r International Journal of Coal Geology 45 (2000) 55–84
63
Table 1
Gippsland Basin — total Traralgon Formation measured coal reserves and inferred coal resources
Field area Žsee Fig. 1.
A ŽOB 0–30.5 m.
B ŽOB 30.5–61.0 m.
C ŽOB 61.0–91.4 m.
Measured Traralgon Formation coal reserÕes in defined coalfields (million tonnes). (Defined coal fields
where: oÕerburden - 91.4 m — see categories A, B, and C below; oÕerburden to coal ratios - 2.0:1;
coal seams - 15.0 m thick included in oÕerburden; coal by definition is - 10.0% ash db)
Loy Yang a
223
49
87
Flynna
167
7
50
South Flynna
489
195
223
Gormandalea
1502
488
84
Melton Park a
23
91
5
Willung a
114
95
69
Holey Plainsa
76
187
40
Coolungooluna
134
645
215
Honeysuckle Hill a
–
111
–
Stradbrokeb
OB categories
not
specified
Longford c
OB categories
not
specified
Boodyarnb
OB categories
not
specified
Won Wrond
OB categories
not
specified
Greenmount d
OB categories
not
specified
Total
2938
2700
1028
Total inferred Traralgon Formation coal resources for the Gippsland Basin (M. tonnes) (includes the
9,664 M.tonnes of measured reserÕes from aboÕe)
T2 coal seamse
no
overburden
limits
T1 q T0 coal seamse
no
overburden
limits
Total all T seams
includes measured
coal reserves
AqBqC
359
224
907
2074
119
278
303
994
111
3700
164
288
2
500
9664
98,002
247,379
345,381
a
Source: Gloe Ž1980..
Source: VBCC Ž1983. updated.
c
Source: Holdgate Ž1987..
d
Source: Gloe et al. Ž1988..
e
Calculated from area isopach maps — Figs. 5 and 6. OB s overburden.
b
equivalent to the mineral matter in black coal technology ŽKiss, 1982.. Ash properties are described
under two major groupings: ash minerals and ash
inorganics ŽKiss and King, 1977, 1979.. The analyses distinguishes between particulate ash minerals
such as SiO 2 from quartz, Al 2 O 3 from clays, and
ash inorganics ŽNa, Mg, and Ca, etc.. that occur as
salts of carboxylic acids. Sodium also occurs as
NaCl dissolved in the bed moisture of raw coal.
Inorganic ash distribution patterns usually reflect
post-depositional migration ŽKing et al., 1983.
whereas ash minerals from clay and quartz increase
rapidly near interseam sediments, overburden, and
towards the margins of seams ŽGloe and Holdgate,
1991.. The minerals Žwhich occur as discrete particles. are expressed as SiO 2 q Al 2 O 3 q TiO 2 q K 2 O
q Fe S 2 ; and the inorganics Žas a group of dilute
HCl extractable or exchangeable cations and watersoluble salts. are expressed as Na q Ca q Mg q Fe
Žnon-pyritic. q Al q NaCl.
Table 3, derived from the data of Gloe Ž1980.,
gives the main mineral ash and inorganic ash constituents for dry coal, by seam, for each of the main
Traralgon Formation coalfield areas in the Latrobe
Valley area. The constituents not included were K,
P, and Ti, as the values were mainly in trace amounts
only. Sulphur values Žfrom SO 3 . are mainly organic
sulphur as generally pyritic and sulfate sulphur are
very low. The figures are derived from many hundreds of bore core analyses, and expressed as
weighted averages per seam and per bore area of
influence for the main coal fields. The more subtle
64
G.R. Holdgate et al.r International Journal of Coal Geology 45 (2000) 55–84
Fig. 5. Isopach thickness map for the T2 coal seams, showing net thicknesses for all seams greater than 3.0 m thick. Lines for cross-sections ŽFigs. 3 and 4. also shown.
G.R. Holdgate et al.r International Journal of Coal Geology 45 (2000) 55–84
Fig. 6. Isopach thickness map for the T1qT0 coal seams, showing net thicknesses for all seams greater than 3.0 m thick. Lines for cross-sections ŽFigs. 3 and 4. also shown.
65
G.R. Holdgate et al.r International Journal of Coal Geology 45 (2000) 55–84
66
Table 2
Weighted averages for Traralgon seam coal properties Žafter Gloe, 1980; Gloe et al., 1988.
Area
Coal seam
Moist %
Ash %db
Vol %db
C %db
H %db
S %db
NWSE
GDSE
LoyYang
Flynn
South Flynn
Gormandale
Melton Park
Willung
Holey Plain
Coolung
Stradbroke
Longford
Boodyarn
Won Wron
Greenmount
T1
T1
T1
T1r2
T1r2
T1r2
T1r2
T1r2
T1r2
T2
T1r2
T2
T1r2
56.4
58.5
57.2
56.3
56.1
54.0
52.5
55.4
58.0
49.3
55.8
48.5
53.1
2.4
2.8
2.5
2.4
3.4
3.0
2.6
2.9
2.8
2.5
4.6
2.6
9.2
49.6
50.1
52.3
52.1
52.4
50.4
47.4
48.4
47.9
46.5
–
–
45.8
69.4
67.7
66.2
66.2
65.8
66.2
68.4
67.7
68.4
70.9
–
66.1
62.7
4.9
4.9
4.7
4.8
4.8
4.8
4.8
4.9
5.2
5.2
–
4.8
4.5
0.51
0.42
0.69
0.87
0.93
0.24
4.59
4.02
1.40
5.30
–
0.20
1.50
10.1
9.2
9.1
9.4
9.4
10.2
11.7
10.3
10.8
13.1
–
–
10.1
28
27.4
26.2
26.4
26.5
26.9
29.2
28.1
26.6
29.3
–
25.9
25.1
Moists moisture, Vol s volatiles, C s Carbon, H s Hydrogen, NWSEs net wet specific energy ŽMJrkg., GDSEs gross dry specific
energy ŽMJrkg., Coolungs Coolungoolun, db s dry basis.
gradations across areas are less apparent due to the
averaging process, but the overall regional trends
remain illustrative of the lateral variability.
To better illustrate the relative changes, Gloe’s
Ž1980. data have been recalculated here to give
relative percentages Žout of 100% ash., rather than
expressed as percentages out of total dry coal. The
following results are evident in Traralgon coal ash
constituents and mineral ash to inorganic ratios from
Tables 2 and 3.
Ža. Mineral ash constituents ŽSiO 2 , Al 2 O 3 and
Fe 2 O 3 . dominate over the inorganic ŽCaO, MgO,
Na 2 O, and Cl. if the introduced organic sulphur
Žfrom marine transgressions from the east. is sub-
tracted. Traralgon seam coals in the Loy Yang–
Flynn–Gormandale area ŽFig. 1. typically have a
ratio of between 1.5:1 and 4.0:1 for mineral ash to
inorganic constituents. To the east in the Willung–
Holey Plains–Coolungoolun fields there is a ratio of
between 2.3:1 and 6.7:1 mineral ash to inorganics.
The values for ash in the T1 and T2 seams appear
similar, although few data are available specifically
on averaged values for the Traralgon 2 seam.
Žb. The high mineral ash ratio represents siliclastic influx Žfloods, storm washover, etc.. into the
swamp environment from nearby fluvio–lacustrine–
barrier sources. The inorganic fraction, which includes salts, is comparatively low when compared
Table 3
Main ash constituents Žrelative%. within the defined Traralgon Formation coal fields Žafter Gloe, 1980.
Area
Seam
Ash in coal
Ž%db.
SiO 2
Al 2 O 3
Fe 2 O 3
CaO
MgO
Na 2 O
S
Cl
LoyYang
Flynn
Traralgon Creek
South Flynn
Gormandale
Melton Park
Willung
Holey Plains
Coolungoolun
T1
T1
T1
T1
T1 q T2
T1 q T2
T1 q T2
T1 q T2
T1 q T2
2.4
2.8
2.1
2.5
2.4
3.3
3.0
2.8
3.5
34
31
25
47
21
19
12
13
7
22
10
32
27
22
11
18
10
10
11
25
10
6
13
12
11
6
4
3
8
3
1
6
16
5
6
0
4
7
7
4
5
9
4
3
0
2
3
2
1
2
2
1
1
0
21
14
20
13
29
29
47
60
76
2
1
2
1
2
2
0
0
1
Ash Ž%db. s total ash in coal on a dry basis, relative ash constituents as percentage in dry coal out of 100% ash; relative abundance of K, P,
Ti, etc, not shown as they are trace amounts only; T1 q T2 s Traralgon 1 q Traralgon 2 seam data combined. Relative % ash data not
available for Stradbroke, Longford, Boodyarn, Won Wron, and Greenmount.
G.R. Holdgate et al.r International Journal of Coal Geology 45 (2000) 55–84
with the younger Morwell and Yallourn seams. This
may be a result of fresh groundwater uptake Žthe
source for inorganic ash — Kiss et al., 1985. into
the peat from low salinities of the underlying sand
aquifers in the Honeysuckle Hill Gravels. Chemical
analysis of Traralgon Formation aquifers water Žincluding the Honeysuckle Hill Gravels. indicates values of less than 80 mgrl total dissolved solids ŽTDS.
ŽBrumley et al., 1981..
occur for Traralgon seams underlying the Lakes
Entrance Formation, and for localised sulphur increases adjacent to some interseam sediments. They
attributed this to post-depositional diffusion from
sulphate-bearing ground waters. Kiss et al. Ž1985.
thought it probable that sulphates derived from marine transgression formed the source for the production in situ of reduced sulphur species H 2 S, Ss , and
S, and their subsequent incorporation in the reactive
coal matrix.
Diessel Ž1992. discussed the problems of distinguishing between syndepositional sulphurs Ži.e.,
sulphur formed within presumably fresh andror
brackish water peat-forming environments during deposition. vs. post-depositional sulphur, derived from
marine water influences following subsequent transgression over the peat swamp. In either case, sulphate-reducing bacteria DesulphoÕibrio desulfuricans and Clostridium desulfuricans, that have a low
tolerance for the higher acidities of fresh-water peats,
function better where high pH Žmore marine influenced. waters occur. The easterly increase in sulphur
in Traralgon Formation coals appears mostly related
to syndepositional effects, although in some areas the
immediately overlying marine beds also post-depositionally add to or modify the sulphur distribution.
6. Sulphur distribution in Traralgon Formation
coals
Sulphur content is at least 0.5% higher in the
Traralgon Formation coal seams than for any of the
younger Oligo–Miocene seams, and increases rapidly
in the east towards Holey Plains Ž4.59%., Coolungoolun Ž4.02%., and Longford Dome Ž5.30%. —
Table 2. By far the most important sulphur source
Ž) 90%. in Latrobe Valley coals is organic sulphur
ŽKiss et al., 1985..
Smith and Batts Ž1974. and Gloe Ž1980. noted
high organic sulphur in Traralgon Seam coals in
selected coastal bores and in the coalfields of Coolungoolun and Holey Plains. Thompson Ž1979. and
Holdgate Ž1980. both described regional sulphur isolines for Traralgon seam coals in the Holey Plains,
Coolungoolun, and Stradbroke Coal Fields, attributing them to the relative position of the overlying
marine-transgressive Lakes Entrance Formation
limestones and marls. Kiss et al. Ž1985. examined
the regional distribution of sulphur in Latrobe Valley
brown coals, noted higher Ž0.4–0.9%. sulphur values
7. Traralgon Formation brown coal lithotypes
All Latrobe Valley coals are prominently banded,
and the different types of bands are referred to as
different brown coal lithotypes. Lithotypes may be
sharply bounded or gradational, and vary from 5 cm
Table 4
Relative abundance Ž%. and average bed thickness Žm. for lithotypes in the Traralgon Formation coal seams
Bore no.
Depocentre location
Lithotype Ž%.
Average bed thickness Žm.
Dark
Medium dark
Medium light
Light
Pale
T2 seam
W200
STR64
Western edge
centre
2
2
37
27
48
57
12
14
1
0
0.83
1.85
T1 seam
W200
STR64
West centre
Main centre
2
2
39
51
54
44
4
2
1
1
0.85
1.49
STR s Stradbroke, W s Willung.
67
68
G.R. Holdgate et al.r International Journal of Coal Geology 45 (2000) 55–84
to 5.0 m in thickness. The layering effects are thought
to indicate original changes in the depositional envi-
ronment, especially water table changes that may
also reflect changes in sea level ŽGeorge, 1975;
Fig. 7. Stratigraphic correlations of Traralgon Formation coal lithotypes in four boreholes, showing coal subseams, sequence boundaries,
systems tracts for T1 coals, and dinoflagellate locations.
G.R. Holdgate et al.r International Journal of Coal Geology 45 (2000) 55–84
Holdgate et al., 1995.. Five lithotypes are recognised
Ždark, medium dark, medium light, light and pale.
that are best seen in the air-dried coal ŽGeorge,
1975.. Each lithotype contains characteristic patterns
of colour, texture, gelification, wood content and
charcoal content. When going from dark to light
lithotypes, moisture decreases up to 5%, but no
apparent ash changes occur ŽGeorge and Mackay,
1991.. Gelification and charcoal mainly occur in the
darker lithotypes. Wood in brown coal varies from
microscopic fragments to tree trunks up to 5.0 m
long, occurring chiefly in the medium light and
medium dark lithotypes. With increased rank, contrasts of lithotype colour decrease, and become less
obvious.
Table 4 summarises the percentages of each lithotype for Traralgon Formation coal seams in two
boreholes, as well as average lithotype bed thickness,
and relative position within the respective coal depocentres Žsee Figs. 5 and 6.. The stratigraphic correlation and coal lithotype succession in four fully
cored lithotype bores is shown in Fig. 7. The changes
in lithotypes for each major seam are as follows.
7.1. The Traralgon 2 seam
This seam has been mainly sampled for coal
lithotypes in two bores; Stradbroke-64 and Willung200 ŽFigs. 5 and 7.. Additional data, not used here,
are also available for Glencoe-47, and Wulla Wullock-7, located towards the northern edge of the
main depocentre. However, interseam splits and erosion Žsee below. mean that the full coal succession is
not present in these latter bores. The Stradbroke-64
bore is located in the central part of the main depocentre trend at Stradbroke ŽFig. 5.. The Willung200 bore is located at Gormandale near the western
boundary margin of the T2 coal seam deposit. The
T2 seam here is demonstrably more thinly banded,
with alternations of medium light to medium dark
lithotypes separated in the middle by a prominent
dark lithotype Žwhich can be correlated to a dark
band at Stradbroke.. The average thickness for lithotype layers Žover the 60.0-m vertical section. is
nearly halved in the Gormandale area, suggesting
that rapid oscillations in the peat depositional environment occur near seam edges, where it may be
69
tectonically less stable. Lithotypes in all the T2
seams sampled appear to be mainly represented by
the lighter varieties.
7.2. The Traralgon 1 seam
Two lithotype bores provide useful representative
data for the T1 seam: Stradbroke-64, located within
the western margins of the main T1 depocentre at
Stradbroke; and Willung-200, located within the central part of the smaller depocentre around the Gormandale area ŽFigs. 6 and 7.. Four lightening-upward cycles are mappable between the two areas,
with boundaries located along interseam partings
andror correlative darker lithotypes Žsee Figs. 6 and
7.. The western depocentre at Gelliondale is noticeably more finely bedded and contains fine-sediment
partings. The main depocentre at Stradbroke splits to
the east and north with interbedded marine shale and
siltstone partings as shown at Wulla Wullock-7 and
Glencoe-47 ŽFig. 6.. Data on the relative abundance
of dark to light coal lithotypes between Gormandale
and Stradbroke ŽTable 4. indicate an easterly increase in the percentage of darker lithotypes. As with
the older T2 seam ŽTable 4., the T1 lithotypes also
display thinner bed intervals towards the seam margin at Gormandale, and a continuation of the less
stable depositional setting in that area. The T1 seam,
however, has a greater overall abundance of darker
lithotypes than the T2 seam. This trend towards
increasing abundance of darker lithotypes follows on
into the younger Oligo–Miocene seams, and was
noted by Kershaw et al. Ž1991..
8. Palaeobotany and petrology of Traralgon Formation coals
Overall, Traralgon coal seams tend to show similar spore–pollen compositions, regardless of seam
age. The highest percentage is pollen from Nothofagus beech forests of the adjacent highlands Ži.e., a
wind-blown pollen component in the Traralgon Formation coal swamps.. Rainforest-dominant swamp
species such as Podocarpaceae and Casuarinaceae
are usually well represented; and other taxa such as
70
G.R. Holdgate et al.r International Journal of Coal Geology 45 (2000) 55–84
Cunoniaceae, Myrtaceae, Elaeocarpaceae, and Proteaceae are also present ŽKershaw et al., 1991.. A
distinctive regional Žclimatically influenced?. pollen
characteristic of the Traralgon 2 seam is its high
Proteaceae values whereas the Traralgon 1 seam has
higher Podocarpaceae and low Proteaceae ŽKershaw
et al., 1991..
In the T2 seam, there is a noticeable differentiation of lithotypes based on pollen composition, lighter
lithotypes have increased Podocarpaceae and lower
Myrtaceae compared to the darker lithotypes. In the
Traralgon 1 coal, going from light to dark lithotypes,
there is a general decrease in the pollen count, and a
decrease in Nothofagus percentages ŽKershaw et al.,
1991.. Petrographic results indicate an increase in
the percentage of coarse plant tissue associated with
the increase in darker lithotypes. The above differences between T2 and T1 coal seams are thought to
be due to an increasingly variable climate ŽKershaw
et al., 1991..
George and Mackay Ž1991. quoted average maceral group Žsubgroup. concentrations in Traralgon
Formation coals at Gormandale and Stradbroke at
67.8% humo-detrinite; 14.7% humo-tellinite; 10.2%
humo-collinite; 6.7% liptinite; and 0.6% inertinite.
9. Marine dinoflagellates within Traralgon Formation interseam sediments
Fossil dinoflagellates are the cysts of microscopic
planktonic algae, which occur today and occurred in
the geological past in a range of aquatic habitats
ŽDodge, 1985.. Dinoflagellate cysts are found in the
interseam strata of the Latrobe Valley Group coal
measures, and are regarded as brackish to marine
water indicators ŽHoldgate and Sluiter, 1991.. Their
presence in interseam sediments of the Traralgon
Formation coals is recorded here for the first time,
and provides supporting evidence for the proximal
marine effects such as those reflected by high sulphur content in the coals. It also assists in palaeogeographic reconstruction.
The SECV Wulla Wullock 7 ŽWW-7. bore southwest of Longford has a continuous core record,
including a number of coal seam splits with interseam sediment layers. The WW-7 bore is located in
an area of thick T1 and T2 coal seams. Thirty-one
samples were taken from each interseam section at
about 3-m intervals. Of these samples, 24 contained
marine dinoflagellates Žsee Table 5 and Fig. 7.. Up
to six taxa were recorded, dominated by Gippslandia
extensa, which is a key Eocene zonal fossil in the
offshore Gippsland Basin ŽPartridge, 1976.. Partridge Ž1990. identified some of the new taxa present
in a typical sample from the T1d interseam in the
WW-7 bore Ž477.9 m.. All taxa identified appeared
to be of marine to brackish-water affinities ŽWilson
and Clowes, 1980; Partridge, 1990; Holdgate and
Sluiter, 1991.. Detailed vertical sampling indicates
that dinoflagellates can occur in abundance throughout a single bed up to several metres thick. Exceptionally continuous dinoflagellate occurrences are
present throughout a number of successive beds for
10 m or more in the T1 interseam sections. The
sediments that contain marine dinoflagellates are dark
brown laminated siltstone and bioturbated siltstone
or mudstone lithofacies. These are more commonly
developed between coal seams in the eastern half of
the onshore Gippsland Basin. However, not all these
lithofacies contain dinoflagellates, and there appear
to be no other indicators of their presence than
obtained by sampling.
In general, the dinoflagellate species recorded
from the Traralgon Formation have little stratigraphic utility in correlations other than as useful
marine palaeoenvironmental indicators ŽHoldgate and
Sluiter, 1991.. However, an Eocene zonal subdivision based on dinoflagellates has been identified for
the offshore Gippsland Basin ŽPartridge, 1976., of
which one of the key zonal species Ž G. extensa. was
identified in the Traralgon Formation onshore. Sun
Ž1991. further noted that the dinoflagellate occurrences in WW-7 samples tended to be associated
with increased numbers of Nothofagus brasii type
pollen, believed to have been introduced as windblown pollen into the lowland swamps from highland-based plants ŽKershaw et al., 1991.. This was
interpreted to indicate marine transgressions of the
lowlands preferentially increased the highland pollen
contribution. Sun Ž1991. also found four samples
from the T2 seam interval contained warm temperature mangrove pollen species of Rhizophora and
Sonneratia, similar to mangrove pollen in equivalent
offshore sediments ŽPartridge, 1976.. At least one of
these four samples contained dinoflagellates.
Table 5
Dinoflagellates in Traralgon coal interseams — WW 7 BoreŽafter Holdgate, 1996.
Number
of
species
466.9
472.5
475.3
477.9
478.8
482.9
483.4
483.8
486.4
488.0
490.9
495.7
496.7
515.1
516.7
523.2
525.8
530.3
533.7
539.4
541.9
561.0
640.7
641.3
1
3
2
4
5
2
2
2
2
4
2
6
1
1
1
1
1
3
1
2
2
1
1
1
Apteodinium
australienmse
Areosphaeridium sp.
Dapslidinium
pastielsii
Deflandrea
druggii
Gippslandia
extensa
Hystrichokolpoma sp.
Nematosphaeropsis sp.
Operculidinium
centrocarpum
Reticulatosphaera
stellata
Saeptodinium
tasmaniense
Spiniferites
bulloideus
S. pseudofurcatus
Wetzelliela sp.
2
11
1
3
1
1
5
4
20
138
242
1
2
1
1
3
7
10
1
7
2
1
1
21
17
5
66
5
3
1
1
1
1
3
1
1
169
173
2
3
2
33
2
7
5
4
3
10
1
1
G.R. Holdgate et al.r International Journal of Coal Geology 45 (2000) 55–84
Depth
Žm.
5
71
72
G.R. Holdgate et al.r International Journal of Coal Geology 45 (2000) 55–84
10. Sequence stratigraphic analysis and palaeogeography of the Traralgon Formation
Sequence stratigraphic analysis is best-applied in
near-shore environments where alternations of marine and non-marine environments occur. The identification of marine interseam transgressions into the
Latrobe Valley ŽHoldgate and Sluiter, 1991; and as
documented above., enables the application of sequence stratigraphic methods to the Traralgon Formation coal measures. Interseam flooding surfaces
can be traced into continuous thick coal seams where
they register as high sulphur dark lithotype coals.
The high-sulphur dark coals usually form the basal
part of coal-lithotype lightening-upward cycles that
were equated to parasequence-scale cycling ŽHoldgate et al., 1995.. They provide a means of carrying
sequence analysis into the non-marine parts of the
basin. A subdivision of existing coal seam nomenclature into subseams Že.g., T1a–T1e. is necessary for
identification of lightening-upward lithotype cycles
Žparasequences..
In general, the coal bearing sequence follows a
vertically repetitive pattern in the Traralgon Formation Žsee WW-7 bore in Fig. 7.. The base of each
sequence lies immediately above an erosional sequence boundary that may cutout parts of the underlying beds, and frequently occurs at the top of the
underlying coal seam. The sediments deposited at the
base of each sequence may comprise thick beds of
coarse sandstones deposited in channel-like configurations on a surface eroded into the underlying Žoften
coally. sequence. Such beds Že.g., the coarse sandstones and conglomerates between the T1 and T2
coals. are interpreted as deposits of the low-stand
systems tract. The coarser facies are usually overlain
by marine transgressive facies of laminated and burrowed siltstones and mudstones Ždinoflagellate bearing., considered herein as part of the transgressive
systems tract. For some sequences Že.g., the T2
sequence., the coarser grained beds at the base are
absent, and transgressive siltstones immediately
overlie the sequence boundary below. The transgressive facies grade up through fine sandstone
Žbarrierrfluvial system. into coal. The remaining
and most dominant component of the sequence consists of semi-continuous coal subseams interbedded
with thin marine Ždinoflagellate-bearing. siltstones,
or simply continuous coal in the main coalfields
up-dip of the interbedding. The semi-continuous coal
subseams appear to prograde eastwards and pinch-out
into sandstone facies of the Dutson Sand Member
ŽFig. 8.. Each successively younger subseam appears
to demonstrate a greater easterly extent. Above the
lowermost fine sandstone Žbarrierrfluvial system.,
the succession is considered to represent the highstand systems tract.
Three main sequences are recognised, which comprise the Traralgon Formation coal measures, and
their facies-equivalent sequences in the onshore and
near offshore Gippsland Basin. They include the T0,
T1, and T2 coal sequences; underlain by the Honeysuckle Hill Gravels and equivalents.
10.1. Middle Eocene Honeysuckle Hill GraÕels and
equiÕalents (Fig. 9a)
The Honeysuckle Hill Gravels ŽFig. 2. lack significant marine incursions. The unit probably includes a
number of sequences, but for convenience is treated
here as representing a single depositional period.
This facies is dominated by fining upward coarse
sandstone and conglomeratic fluvial to outwash alluvial fan sequences, that represent a high energy,
polycyclic, quartzose, sedimentary environment that
covered most of the onshore Gippsland Basin south
of the Rosedale Fault in the early phase of basin
development. Minor coal seams in this unit are
referred to as the Aolder coal seamsB on the crosssections ŽFigs. 3 and 4.. Thickened gravel deposits
of the Honeysuckle Hill Gravels were located along
the east trending nose of the Balook Block, and
interbed to the south with coarse sandstones and
minor shales. Adjacent relief along the Palaeozoic
basin margins provided most of the sediment source
ŽBolger, 1979a,b; Holdgate, 1980.. Lithic fragments
of Mesozoic age are rare to absent, suggesting there
was little relief in the adjacent Mesozoic Balook
Block at the time. Taylor Ž1986. described a nonmarine limit for the base of the Middle Eocene Ž P.
asperopolus-base N. asperus Zones. shortly east of
Barracouta ŽFig. 9a.. Beyond this is a transitional
region ŽOmeo and Flounder lagoon areas. where
interpreted brackish-estuarine marshes with interbedded greensand units appear. In the Kingfish oil field
G.R. Holdgate et al.r International Journal of Coal Geology 45 (2000) 55–84
73
Fig. 8. Isopach thickness map for the Dutson Sand Member.
area, peripheral to a central southeast trending
Fortescue Embayment, episodic coarsening upward
shallow marine transgressive barriers, dunes, beaches,
and greensands contain poor marginal marine
74
G.R. Holdgate et al.r International Journal of Coal Geology 45 (2000) 55–84
Fig. 9. Palaeogeography maps for the Gippsland Basin for time intervals: Ža. Honeysuckle Hill Gravels — base Middle Eocene Ž48.0 Ma.; P.asperopollus —base N. asperus
Zone; Žb. T2 coal — top Middle Eocene Ž40.0 Ma.; top Lower N. asperus Zone; Žc. T1 coal — Late Eocene Ž37.0 Ma. — Middle N. asperus Zone; Žd. T0 coal —
Eocene–Oligocene boundary Ž36.0 Ma.; Upper N. asperus Zone.
G.R. Holdgate et al.r International Journal of Coal Geology 45 (2000) 55–84
foraminiferal faunas. The marine transgressions appear to have come from the southeast.
10.2. The Traralgon 2 (T2) sequence (Fig. 9b)
10.2.1. Boundary relationships and distribution
The T2 sequence forms the lowest major coalbearing interval of the Traralgon Formation in the
onshore Gippsland Basin. The base of the T2 sequence commences with the first known marine
transgression in the onshore Gippsland Basin, directly on to a weathered Žpalaeosol?. surface of the
older coal seams marker horizon ŽFigs. 5 and 6..
This marine transgression, as defined by marine
dinoflagellate-bearing siltstones, was cored in WW-7
bore at 641.3 m ŽFig. 3.. The top of the T2 sequence
is placed immediately beneath a fining-upward sandstone-conglomerate unit, correlated regionally from
bore data, essentially separating the T1 and T2 coal
seams Žlocally eroding parts of the T2 seam..
10.2.2. Main lithologies and facies
The T2 sequence averages approximately 100.0 m
in thickness, most of which comprise the T2 coal
seams as recognised through much of the Seaspray
Depression and Baragwanath Anticline. The coal
component of the sequence is best developed in an
east–west trending coal depocentre extending from
Gormandale and Stradbroke coal fields for at least
75.0 km to the Golden Beach gas field offshore ŽFig.
5.. The coal depocentre coincides with the axis of
the Baragwanath Anticline, with the thickest coal
developments being ) 80.0 m in the west near
Stradbroke, and a second coal-thick Ž) 80.0 m. at
Longford. Towards the present coast, the T2 seams
thin and split into subseams. Offshore, the sequence
becomes mostly sandstone at the Barracouta gas
field, where it constitutes the main reservoir facies
ŽFig. 3..
Normal faulting of the Rosedale Fault, delimits
the coal phase to the north, andror this age sequence
has been stripped from this northern area. As this
fault also influences the northern extent of the underlying outwash fans of the Honeysuckle Hill Gravels
it is likely it formed a structural boundary to Early
and Middle Eocene deposition. By the Late Eocene,
Rosedale Fault movements appear to cease, and sedimentation spread into the northern areas. In sequence
75
analysis terms the cored section in WW-7 bore ŽFig.
7. indicates a late transgressive systems tract event
forms the base of the T2 sequence, becoming more
dominantly coal rich upwards. Therefore, T2 coals
develop and outbuild primarily within the interpreted
highstand systems tract ŽFigs. 3 and 4.. Calculations
of the total coal resource Žseams ) 3.0 m thick.
contained within the T2 isopach map ŽFig. 5. amounts
to approximately 98 Gt ŽTable 1., of which approximately 425.8 Gt are measured coal reserves.
10.2.3. T2 age and sequence correlation
The T2 sequence is confined by palynological
dating to the Lower N. asperus zone ŽPartridge,
1971, 1978a,b, 1997; Partridge and Macphail, 1997;
Stacy, 1979; Whitelaw, 1983; Macphail, 1990a,b;
Morgan, 1991; Sun, 1991., in the offshore area
ranging in age from 39.5 to 48.0 Ma. ŽHaq et al.,
1988.. In the onshore, additional constraints to this
age range are provided by the presence of marine
dinoflagellates in interseam siltstones consistent with
the Deflandrea heterophylcta dinoflagellate Zone,
which offshore ranges between 39.5 and 41.2 Ma.
ŽHaq et al., 1988; Stover and Partridge, 1973; Partridge, 1976.. At least two sequences occur within
this time range to which the T2 sequence could
belong ŽHaq et al., 1988.. Here it is proposed that
the T2 sequence best commences at the Middle
Eocene transgressive deposits Žafter Haq et al., 1988.
dated at 41.2 Ma. and finishes at the end of the
succeeding high-stand deposits dated at 40.5 Ma
Ži.e., a range of ca. 0.7 Ma.. ŽFig. 2.. This would
give an average Žcompacted. sedimentation rate of
7000 yearsrm ŽTable 6.. The major sea level fall
dated ŽHaq et al., 1988. at 39.5 Ma. approximates to
the sequence boundary event at the top of the T2
Table 6
Sequence ages, ranges, and interpreted rates of accumulation for
Traralgon coals — onshore Gippsland
Sequence Age range Total years Brown coal Peat accum
Žyearsrm. Žyearsrm. accum rate rate Žyearsrm.
Žyearsrm.
T1
37.0–37.5 0.5
5000
T2
40.5–41.2 0.7
7000
Gippsland Peats a
1760 years –
a
2000
2800
2700
Kershaw et al., 1993; accum saccumulation.
76
G.R. Holdgate et al.r International Journal of Coal Geology 45 (2000) 55–84
sequence, and with the palynology zone boundary
between Lower and Middle N. asperus Zones ŽFig.
2.. In terms of correlation with other nearby basins,
this sequence probably correlates with the development of a number of coals in southern Australian
Basins including the A seam at Anglesea ŽTorquay
Basin.; the Kingston seams ŽOtway Basin.; and the
Lower Werrilup seam ŽBremer Basin. ŽHoldgate and
Clarke, 2000..
10.2.4. Coal characteristics
Coals of the T2 sequence have the lowest moisture content Žoften between 50 and 55%. of any of
the seams in onshore coalfields. When buried over
550.0 m such as at WW-7 bore, moisture content
averages about 47% Žunpublished SECV coal analysis data.. T2 coal lithotypes in four bores ŽFig. 7.
were reported to be less clearly defined due to rank
increase than for the overlying T1 coal seams, and to
comprise more compact and gelified coals, mostly of
medium light and medium dark lithotypes ŽHiggins
et al., 1981; Kiss et al., 1984.. The coal lithotype
successions at Gormandale, Stradbroke and WW-7
appear to include at least four to five parasequences,
each about 15.0–20.0 m thick, separated at prominent dark lithotypes ŽFig. 7.. Sulphur content can
exceed 4% at Coolungoolun and on the Longford
Dome ŽGloe, 1980; Holdgate, 1987. where coal splitting and marine influence is pervasive.
10.2.5. Offshore palaeogeography
Taylor Ž1986. described a more regressive marine
limit for the top Middle Eocene Žtop Lower N.
asperus Zone. extending along a similar trend as the
T2 coal depocentre out to the Kingfish oil field,
where episodic transgressive barrierrdune complexes occur ŽFig. 9b.. The transitional Omeo and
Flounder lagoonal areas continued to form near
Bream, and as the TunarFlounderrMarlin channels,
where brackish-estuarine marshes and greensand environments occurred. Marine ingressions appear to
have come from the southeast and headed for the
Opah Channel area.
10.3. The Traralgon 1 sequence (Fig. 9c)
10.3.1. Boundary relationships and distribution
The T1 sequence includes the second major coalbearing interval of the Traralgon Formation in the
onshore Gippsland Basin succession. The base is
marked by a regionally widespread sandstone-conglomerate aquifer interval on to the top T2 boundary
surface below ŽFigs. 3 and 4.. The aquifer appears
on bore data to infill an apparent relief surface on
top of the underlying T2 sequence of 20.0 m or
more. The top of the sequence is taken as the top of
the T1 coal seam or subseam split. In the nearshore
and offshore areas, the T1 and T0 coal subseams thin
and split into a major sand interval, the Dutson Sand
Member, where definition of the T1–T0 boundary
relies on palynological age control. An isopach map
of the Dutson Sand Member Žincludes minor coals
usually - 5.0 m thick. ŽFig. 8. indicates an elongated north–south sandstone body seaward to the
main coal depocentres ŽFig. 6., extending north–
south for 80.0 km. South of Dutson it trends offshore. It has an average width of 10.0 km. A depocentre to the sequence around the Dutson Downs
area contains up to 200.0 m thickness, as in Dutson
Downs-1 well. The Dutson Sand Member is poorly
sampled, with cuttings mainly comprised of medium
grained sandstones. Coarsening upward gamma ray
log signatures suggest it comprises several stacked
barrier systems. Sandstones of the Dutson Sand
Member appear to constitute the major hydrocarbon
reservoirs at the Golden Beach Gas Field shortly
offshore ŽFig. 3..
The isopach map ŽFig. 6. shows the distribution
of the combined T1 and T0 coal seams. The coals
cover an area 80.0 km long by 40.0–60.0 km wide,
mainly south of the Latrobe River and on the Baragwanath Anticline. Up to two-thirds of the total thickness can constitute coal, with major coal depocentres
up to 100.0 m thick in the Flynn’s Creek Syncline,
and the Gormandale and Stradbroke Coal Fields. T0
coals constitute significant proportions of the resource on the north side of the Rosedale Fault near
Sale and Lake Wellington. The T1 sequence extends
further updip into the Latrobe Valley than does the
T2 sequence, with the western limit at the Morwell
MonoclinerFault. Calculations of the total coal resource for seams greater than 3.0 m thick contained
within the T1 q T0 isopach map ŽFig. 6. amounts to
approximately 247 Gt ŽTable 1., of which approximately 540.6 Gt are measured coal reserves.
The T1 seam formed in an extensive back barrier
swamp behind the Dutson Sand Member coastal
G.R. Holdgate et al.r International Journal of Coal Geology 45 (2000) 55–84
sand barrier system. Depositional axis for the T1
seam ŽFig. 6. appears to follow a more north–south
orientation than the T2 Seam, with the main depocentre trending southwards from the Sale township
area. The area of original swamp development had
significantly extended when compared to the more
structurally controlled T2 seam below, suggesting
that basin subsidence was becoming more widespread
and uniform. Where the T1 and T2 coal seams
exceed 60.0 m they are mostly vertically stratigraphically offset, suggesting that differential compaction
of thicker areas of T2 seam may have created sufficiently depressed areas to become sediment sinks
during T1 times. This feature is better developed in
the later Miocene seams ŽHoldgate, 1984..
10.3.2. Main lithologies and facies
The T1 sequence begins with deposition of a
regional incised valley-like fill of coarse-grained
lithofacies up to 20.0 m in thickness. The infill
appears a response to lowering of base levels, and
the upward fining coarse sandstones and conglomerates are taken to indicate a fluviatile depositional
environment ŽHoldgate, 1980, 1987; Whitelaw,
1983.. Erosion of the valley floors removed underlying parts of the T2 coals. At the top of the valley fill
and extending across the interfluve areas is a marine
flood surface characterised by dinoflagellate bearing
siltstones. In the core of bore WW-7 the unit comprises a 5.0-m thick interval, between 538.0 and
543.0 m ŽFig. 7.. The marine flooding event appears
to correspond to a late-transgressive sequence tract
andror condensed interval. The remaining approximately 60.0–70.0 m of the T1 sequence is composed
of at least four main subseam parasequences ŽT1a–
T1d., forming a predominantly coal-rich sequence of
a high-stand systems tract. In the WW-7 bore, each
parasequence begins with dinoflagellate bearing laminated, and bioturbated siltstone facies ŽFig. 7.. Each
parasequence becomes more coal-rich towards the
top, demonstrating a progradational character Žsee
Figs. 3 and 4.. The parasequences updip coalesce to
form up to 70.0 m of continuous coal at Stradbroke
and Gormandale, and in the Flynn’s Creek Syncline.
In the distal ends of the T1 depocentres east of
Gormandale and to the west of Loy Yang, the interseam sediments of the T1 seam commonly occur as
10.0–20.0 m thick fining-upward massive sandstone
77
lithofacies. Although no detailed studies have been
undertaken of these sandstones, Whitelaw Ž1983.
considered their origin at Gormandale to have been
within a fluvial environment. Near the Holey Plains
and Coolungoolun coal fields they can be traced as
discrete aquifer beds for over 25.0 km, suggestive of
braided stream sheet-like sand deposits ŽHoldgate,
1980.. West of Loy Yang, the T1 coals thin to zero.
They are interbedded with up to 200.0 m of
medium-grained sandstones that appear to demonstrate fining-upward gamma ray log signatures, and
were presumably derived as high-energy fluvial
channel systems, of upper coastal plain environment.
10.3.3. T1 age and sequence correlation
The T1 sequence is confined by palynological
dating to the Middle N. asperus Zone ŽPartridge,
1971, 1978a,b, 1997; Partridge and Macphail, 1997;
Stacy, 1979; Whitelaw, 1983; Macphail, 1990a,b;
Morgan, 1991; Sun, 1991., and in the offshore areas
this zone ranges in age between 36.5 and 39.5 Ma
ŽHaq et al., 1988.. This time period includes two
complete sequences as defined by Haq et al. Ž1988.,
with boundary ages of 37.0 and 38.0 Ma ŽFig. 2.. As
the coastal onlap curve shows increasing onlap in the
direction of younging, the T1 sequence onshore Žin
this interpretation. most readily correlates with the
sequence between 37.0 and 38.0 Ma. The T1 coal
itself falls largely within the high-stand systems tract
dated between 37.0 and 37.5 Ma. This gives a
depositional period of 0.5 Ma, with an averaged
compacted coal sedimentation rate of 5000 yearsrm
for 100.0 m of coal. A pre-compacted peat deposition rate of 2000 yearsrm is obtained, Žassuming the
peat to be 2.5 times the coal thickness; Holdgate et
al., 1995. ŽTable 6.. Probably this deposition rate
can be increased further if more time was taken up at
the parasequence boundaries.
10.3.4. T1 coal lithotypes
At Gormandale, the Willung-200 bore recorded
58.0 m of T1 coal, constituting 54% medium light
and 40% medium dark lithotypes ŽFig. 7.. The remaining 6% include dark, light and pale lithotypes,
and wood horizons ŽKiss et al., 1984.. A prominent
dark woody band at around 80.0 m in the middle of
the seam contained interbedded siltstones and inferior coals Ž) 10.0% ash db., and corresponds to the
78
G.R. Holdgate et al.r International Journal of Coal Geology 45 (2000) 55–84
boundary of two parasequences. Other boundaries
are represented by prominent dark lithotypes. A
lithotype log of Traralgon coal in bore Stradbroke-64
ŽHiggins et al., 1981. recorded part of the T1 seam,
but here the T1 and T2 appear to have merged. The
interpreted correlation with other lithotype bores ŽFig.
7. suggests that the sequence boundary between the
T1 and T2 occurs between a medium dark and light
lithotype at 68.5 m. This implies the T2e and part of
T2d subseams were removed Žerosion. at the sequence boundary. It also implies the transgressive
and high-stand interseam sediments pinch out on the
Stradbroke coalfield high. In consequence, all T1
and T2 coals have amalgamated giving an Žeffective.
net continuous coal thickness of 122.0 m at Stradbroke-64. The Stradbroke lithotypes are similar to
those at Gormandale, composed predominantly of
medium light and medium dark coals.
10.3.5. Offshore palaeogeography
Taylor Ž1986. described a more transgressive marine period for the Late Eocene ŽMiddle N. asperus
Zone. extending marginal marine sediments a short
distance west of the Barracouta gas field ŽFig. 9c..
Episodic transgressive barrier systems formed along
a shoreline through the Seahorse, Golden Beach,
Dolphin, Perch, and Kyarra areas along a similar
trend to the T1 coal depocentre. Offshore, sandstone
facies continued to accumulate in the Kingfish area,
and indicate either offshore islands or shallow submerged sandbanks. Transitional to marginal marine
Omeo estuarine systems replaced previous lagoonal
areas west of the Bream Field. The record for the
TunarFlounderrMarlin and Opah shallow-marine
channels is poor due either to later erosion or nondeposition, although it is believed that this channel
system was the centre for most of the marine transgressions coming from the southeast.
10.4. The Traralgon 0 coal sequence (Fig. 9d)
10.4.1. Boundary relationships and distribution
The T0 coal sequence contains less abundant coal
seams and more sands, except north of the Rosedale
Fault where seams over 60.0 m are developed. The
thicker T0 coals north of the fault suggests fault
re-activation, but reversed in sense of movement to
the T2 sequence. T0 coals on the Baragwanath Anti-
cline are poorly represented due to Pliocene uplift
and erosion, except in localised synclines, e.g. the
Gormandale Syncline and Latrobe Valley. Coals of
the T0 sequence are included in the isopach map
ŽFig. 6.. In the Lake Wellington and Seaspray Depressions the top of the sequence in bore logs is
defined as the base of a regional high gamma log
peak marking the base of the overlying Giffard
Sandstone or Lakes Entrance Formation. Offshore,
an equivalent age interbedded coal and sandstone
unit to the T0 sequence has been mapped from
seismic data by Blake Ž1986., and is included in the
isopach thickness map of Fig. 8.
10.4.2. Main lithologies and facies
In the main Dutson Sand depocentre the T0 sequence comprises two to three coarsening-upward,
non-calcareous fine to medium-grained sandstones,
with a series of coal seams up to 5.0 m thick near the
top. The coals amalgamate to over 60.0 m immediately north of the Rosedale Fault. The T0 coals in the
Gormandale Syncline can be up to 35.0 m in thickness, and have a weight average moisture content of
56.0% and an ash content of 3.62% ŽGeorge, 1965..
Similar moisture and ash values were obtained for
T0 coals at Loy Yang. From the subsurface facies
architecture, seismic character, and coarsening-upward gamma log signature, the sequence appears to
have been deposited as an interbedded shoreface
barrier and back-barrier swamp deposit analogous to
the present day Ninety-Mile Beach barrier system.
The complete succession appears to form a series of
stacked aggradational transgressive to high-stand
parasequences.
10.4.3. Age of T0 and sequence cycle correlation
The T0 sequence is dated by the Upper N. asperus palynological Zone ŽPartridge, 1971, 1978a,b,
1997; Partridge and Macphail, 1997; Stacy, 1979;
Whitelaw, 1983; Macphail, 1990a,b; Morgan, 1991;
Sun, 1991. at the end of the Late Eocene. Most of
the sequence is interpreted to comprise the transgressive and high stand systems tract dated by Haq et al.
Ž1988. between 36.5 and 36.0 Ma, based on the
Upper N. asperus Zone range as between 35.0 and
36.5 Ma ŽHaq et al., 1988.. The sea level fall and
sequence boundary dated at 36.0 Ma probably terminated coal deposition for the T0 coal and for the
G.R. Holdgate et al.r International Journal of Coal Geology 45 (2000) 55–84
Traralgon Formation. By the Early Oligocene, marine carbonate sediments had transgressed over the
whole of the eastern half of the onshore Gippsland
Basin.
10.4.4. Offshore palaeogeography
A transgressive marine onlap continued to the
Eocene–Oligocene boundary ŽUpper N. asperus
Zone., depositing biogenic carbonate limestones and
marls over the T1 barrier systems almost to the
onshore part of the basin ŽTaylor, 1986.. In the
offshore Gippsland Basin, such beds are mainly referred to as the Gurnard Formation, which yields a
P17–18 foraminiferal zone age. The microfossil
palaeobathymetric interpretation suggests that much
of the offshore basin sediments were deposited at
water depths less than 50.0 m, but in the
KingfishrMackerelrHalibut area the depths may
have been greater than 50.0 m ŽFig. 9d..
11. Discussion
In the Traralgon Formation thick brown coal seam
developments occur within two sequence third order
cycles ŽHaq et al., 1988.. These include the ŽT2. late
Middle Eocene sequence cycle TA3.5 Ž40.5–42.5
Ma. and the ŽT1. Late Eocene sequence cycle TA4.2
Ž37.0–38.0 Ma.. A third cycle, the ŽT0. TA4.3
Ž36.0–37.0 Ma. spread maximum coal development
over two successive third-order cycles and produced
for multi-seam stacking in the Gippsland Basin.
Palaeolatitudes for the southern Australian coastline
at this time were between 558 and 608S, using the
sea-spreading reconstructions of Veevers Ž1986..
Palaeotemperatures in the Early and Middle Eocene
were warm: ) 208C mean annual as indicated by
O 18 rO16 ratios, but variable, compared to the previous, elevated Palaeocene temperatures ŽBowler,
1982; Truswell and Harris, 1982, McGowran,
1989a,b.. An estimate on annual mean temperatures
for southern Australia in the Middle Eocene Žbased
on palynoflora. were at least 17–188C, with a mean
annual precipitation of at least 1500 mm ŽSluiter,
1991.. The earliest strong evidence for East Antarctic glaciations appears in the Middle Eocene record
ŽAbreu and Anderson, 1998.. The glaciation is considered to have been the result of the progressive
79
thermal isolation of Antarctica due to the opening of
oceanic passages between Antarctica, Australia, and
South America, and the development of strong upper
sea surface circum-Antarctic circulation ŽDomack
and Domack, 1991; Macphail et al., 1993; Zachos et
al., 1993.. Deep-sea circulatory patterns could not
occur until the rupture of the South Tasman Rise in
the Oligocene ŽRoyer and Rollet, 1997..
The widespread Eocene coal swamps along southern Australia margins ŽHoldgate and Clarke, 2000.
suggest a high precipitation than today, possibly
resulting from the influence of rain-bearing westerly
winds triggered by the newly forming circumAntarctic current ŽBerggren and Prothero, 1992.. The
high latitude locations, together with high temperatures, require a greatly expanded subtropical belt.
The existence of a bight between Gippslandr
Tasmania and the Campbell Plateau ŽAntarctica and
Australia being closer together., providing for a large
estuarine basin with salinity imbalances due to stream
discharge and tidal pressures, situated in a rainbelt
ŽTaylor, 1986; McGowran, 1989b.. By the Late
Eocene micro- to mesothermal rainforest flora were
established in southern Australia. This vegetation
pattern equates to palaeotemperatures of 15–218C
ŽCarpenter and Pole, 1995.. The cooling trend culminated in the earliest glaciation on the Australian
continent in the earliest Oligocene ŽMacphail et al.,
1993..
Australia–Antarctica rifting is seen to change at
sea floor spreading Anomaly 19 Žlate Middle
Eocene., when global plate reorganisation occurred
in response to the IndiarAsia collision ŽMcGowran,
1989a.. Transgression in the upper part of Foraminiferal Zone P12 Žlate Middle Eocene. correlates
to the late part of sequence cycle TA3.4 or the
transgressive systems tract of the following sequence
cycle TA3.5. Commencement of T2 coal deposition
ŽLower N. asperus Zone. begins in sequence cycle
TA3.5. Further coal deposition was associated with
the Middle and Upper N. asperus Late Eocene transgressive and high-stand events of TA4.2 and TA4.3
Žtypified by the T1 and T0 coals in Gippsland.. In
the Gippsland Basin the thicker coals appear to
associate mainly with high-stand systems tracts, with
local coal thicks controlled by movements on the
Rosedale Fault. The coals also associate with a series
of rapid rises and falls in sea-level immediately
80
G.R. Holdgate et al.r International Journal of Coal Geology 45 (2000) 55–84
preceding the widespread cooling Žas determined
from the oxygen isotope record., at the Eocene–
Oligocene boundary ŽShackleton, 1984.. Widespread
coal development did not occur until the MidMiocene climatic optimum Ž15.0 Ma later., except
within the Latrobe Valley and Alberton embayments
of the Gippsland Basin. Here, the M2 and M1B coals
were constrained behind maximum transgressive barrier systems located between Rosedale and Sale ŽFig.
10. — sequence cycles TA4.5 and TB1.4. Elsewhere
widespread marine carbonate deposition, that accompanied Late Oligocene transgressions, characterised
the rest of basin.
The Eocene Traralgon Formation coal seams substantially exceed in area any of the later Oligocene–
Early Miocene Latrobe Valley brown coals ŽFig. 10.
in the Gippsland Basin. The younger coals were
similarly thick ŽHoldgate et al., 1995., but were
more constrained by the rising basin margin highlands on the west, and transgressive limits of the
Oligo–Miocene shoreline to the east. Nevertheless,
they aggregate over 135 Gt of resources, of which 30
Gt are categorised as measured reserves ŽGloe, 1980;
Holdgate, 1984.. Clearly, controls on the relative
positioning of the shoreline facies are critical to the
Gippsland Basin brown coal deposits and their rela-
Fig. 10. Major coal depocentres Žcoal ) 80.0 m. in the Gippsland Basin from Eocene to Miocene coals.
G.R. Holdgate et al.r International Journal of Coal Geology 45 (2000) 55–84
tive areal extent, as the seam thicknesses Žassuming
roughly constant subsidence rates. of about 60.0–
100.0 m generally appear similar.
12. Conclusions
The Traralgon Formation in the Gippsland Basin
is outstanding in its contained resources of brown
coal. Thick, low-ash coals accumulated behind
shoreline sandstone barrier facies. Episodic marine
transgressions interrupted the coal deposition for up
to 30.0 km inland. The major coal deposits were the
T2, T1, and T0 coal seams and subseams that form
continuous coal seams over 100.0 m thick. Organic
sulphur content in the coal is primarily related to
marine proximity, as controlled both syn-depositionally by relative degree of marine coastal onlap, and
post-depositionally by overlying marine transgressions. The furthest inland coals have the lowest
sulphur content and comprise the majority of the
proven coal reserves. The vertical successions of
brown coal lithotypes show rapid alternations towards the basin margins and more uniform less
changeable conditions in the main depocentres.
A sequence analysis of the coal seam stratigraphy
suggests that each major seam is confined to within
one sequence, and parasequence cycling is shown
by lightening-upward coal-lithotype successions. Palaeogeographic reconstructions suggest that each
seam includes a subseam and interseam facies suite
that varies from inland fluvial influenced environments to extensive coastal plain facies with episodic
marine influence. Marine sandstones equivalent to
the Traralgon Formation coals appears to form some
of the main reservoir facies to the oil and gas fields
in the offshore Gippsland Basin. A significant baselevel fall and erosional surface, interpreted as a
sequence boundary, separates the late Middle Eocene
T2 coal from the late Upper Eocene T1 and T0 coals.
This surface, together with the coal seam palynology
ages, can be tied to the relative coastal onlap curves
of Haq et al. Ž1988., and provides a means of
deriving peat accumulation rates. The huge coal
resources and reserves of the Traralgon Formation
constitute one of the single biggest brown coal deposits in the world.
81
Acknowledgements
This research forms part of an ARC funded study
into the evolution and development of non-tropical
continental shelf and basin sediments in southeastern
Australia. The coal analysis data is open file information from drilling results undertaken by the former State Electricity Commission of Victoria. The
authors wish to acknowledge the useful referee comments from R.M. Flores and C.R. Ward.
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