Geological Society of Australia
ABSTRACTS Number 2
AUSTRALASIAN SEDIMENTOLOGISTS
GROUP C O N F E R E N C E CANBERRA DEC 1-2 1980
AUSTRALASIAN SEDIMENTOLOGISTS GROUP CONFERENCE CANBERRA, A.C.T. DECEMBER 1980
ABSTRACT VOLUME EDITED BY PETER J. COOK
1
CONTENTS PAGE
PROGRAM
ASG 19 80 CONFERENCE
PROGRAM
ABSTRACTS
Introductory Comments 1.
QUATERNARY TEMPERATE SHELF SEDIMENTATION. J.F. Marshall & P.J. Cook. The petrology and geochemistry of iron and phosphorus-rich nodules from the continental shelf of northern New South Wales
2.
u
SALINE LAKES SEDIMENTATION J.M. Bowler. Continental evaporite Quaternary hydrologic
fades and their evolution cycles.
through
P. De Dekker, R.V. Burne, J. Bauld & J. Ferguson. Saline
lakes of the Eyre Peninsula,
South
Australia.
L.A. Chambers, Ferguson & R.V. Burne. Sedimentology lake3 Spencer
and geochemistry Gulf.
of a coastal athalassic
saline 19
A.R. Milnes. Studies
of calcretes
in South
21
Australia.
B.C. Youngs. Sediments from a Cambrian South Australia.
alkaline
lake, Officer
Basin.3 23
2 PAGE J.M. Bowler. Classification and hydrologic response of selected Australian salt lakes.
25
J. Dulhunty. Quaternary deflation of Lake Eyre and development of the Simpson and Tirari deserts.
27
C.R. Lawrence. Salt lakes as groundwater discharge zones in northwestern Victoria and northern Chile.
29
J. Dulhunty. Eolocene sedimentation in Lake Eyre.
30
P.G. Macumber. Hydrochemical and hydrodynamical processes in the salt lake basins of northwestern Victoria. 3.
33
EPEIRIC SEA SEDIMENTATION B. Murrell. Late Froterozoic magnesite sedimentation - an epeiric sea or saline lake in South Australia.
36
B.M. Radke. Models for cyclic sedimentation in epeiric carbonates of the Georgina Basin.
37
P.S. Moore. Fine grained clastic sedimentation in an epeiric sea - a model from the Cambrian of South Australia. 4.
39
TASMAN GEOSYNCLINE SEDIMENTATION K.A.W. Crook. Fore-arc models and Fhanerozoic flysch - fallacy or fundamental insight?
42
R. Cas. Falaeogeographic evolution of the L.F.B. of S.E. Australia and constraints on the choice of tectonic models.
44
C. McA. Powell. The growing Lachlan Orogen reflected in sediments of the northern Lachlan Fold Belt.
46
R.A. Glen. Devonian sediments of the Cobar Basin - transition from turbidite to fluviatile deposition.
47
PAGE
3
D. Hilyard. Mullions Range voloanics - stratigraphy and palaeogeogrphy.
49
J.W. Pemberton. The stratigraphy of the volcanic rocks of the Cudgegong District, N.S.W.
51
R. Bhatia. Rare earth element geochemistry of clastic rocks of the Tasman Geo sync line.
53
M. Garratt. Trough, Victoria.
54
Some problems in the Mount Read Volcanics3 a Cambrian rhyolite-dacite-andesite complex in Western Tasmania.
5b
Depositional
model for the Melbourne
K. Corbett.
R. Williams. Trough
sedimentation.
Criteria for distinguishing submarine
fan and base-of-slope deposits3 Western and South Western Tasmania. 57 P.J. Conaghan, J.G. Jones, K.L. McDonnell, and K. Koyce. Dynamic fluvial basin model for the Permo-Triassic Sydney Basin.
59
C. Fergusson. Sedimentology of the Late Palaeozoic Coffrs Harbour Beds3 north-eastern N.S.W.
61
R.J. Korsch. Petrofacies and petrologic evolution of sandstones in Coff's Harbour Block3 New England Orogen.
62
J. Fergusson. Palaeogeographic significance of Late Carboniferous Pyroclastics3 Werrie Syncline3 N.S.W.
64
D. Lindley. Early Carboniferous sedimentation in the Southern New England Belt. 65 5.
POSTER SESSIONS
K.A.W. Crook. Tectonic controls on the distribution of Lambian Fades
basins
in NSW and Victoria.
67
K.A.W. Crook. Fore-arc evolution and continental growth - a general model.
69
P.F. Carr & B.G. Jones. Lower Devonian volcanics at Marulan, NSW.
71
J. Carey. Holocene sediments and molluscs in Sydney Harbour.
73
R.V. Burne. Sedimentology of Spencer Gulf. R.A. Cas, C. & J. Fergusson, J.G. Jones, C.McA. Powell, W.D. Roots The Kowmung Volcaniclastics: A deep-water succession of mass flow origin, north-eastern Lachlan fold belt, NSW. FIELD GUIDE 1.
M. Owen & R.A. Cass. Siluro-Devonian volcanogenic sedimentation in the Lachlan Fold Belt.
5 ASG
1980
CONFERENCE
PROGRAM
Sunday 30 November 6.30 - 9.30 p.m.
Registration and setting up of poster displays (Building 3).
Monday 1 December 8.30 a.m.
Registration
9.00
J.F. Marshall and P.J. Cook.
The petrology and geochemistry of iron and phosphorus-rich nodules from the continental shelf of northern New South Wales. 9.30
Jim Bowler, Dept. of Biogeography and Geomorphology, Research School of Pacific Studies, A.N.U.
Continental evaporite fades and their evolution through Quaternary hydrologic cycles. 10.00 CO
Q)
10.30 11.00
P. De Dekker, R.V. Burne, J. Bauld & James Ferguson, B.M.R.
Saline lakes of the Eyre Peninsula3 South Australia. Morning tea
£
TO £
Lyn A. Chambers, Baas-Becking Geobiology Lab. and R.V. Burne).
(with James Ferguson
Sedimentology and geochemistry of a coastal athalassic saline lakey Spencer Gulf.
11.30
A.R. Milnes, C.S.I.R.O. Division of Soils.
12.00
Bridget Youngs, S.A. Oil and Gas Corporation.
Studies of calcretes in South Australia. Sediments from a Cambrian alkaline lake3 Officer Basin, South Australia. 12.30
Barbeque lunch
CO
Co
B. Murrell, C.R.A. Exploration.
Late Proterozoic magnesite sedimentation - an epeiric sea or saline lake in South Australia. B.M. Radke, B.M.R.
•r* &
Models for cyclic sedimentation in epeiric carbonates of the Georgina Basin. P.S. Moore.
Fine grained clastic sedimentation in an epeiric sea - a model from the Cambrian of South Australia. Afternoon tea K.A.W. Crook, Geology Department, School of General Studies, A.N.U. £ r-i S) £ CO
0
£
1
co £
Fore-arc models and Phanerozoic flysch - fallacy or fundamental insight? Ray Cas, Department of Earth Sciences, Monash University.
Palaeogeographic evolution of the L.F.B. of S.E. Australia and constraints on the choice of tectonic models. C. McA. Powell, School of Earth Sciences, Macquarie University
The growing Lachlan Orogen reflected in sediments-of the northern Lachlan Fold Belt. R.A. Glen, Geological Survey of N.S.W.
Devonian sediments of the Cobar Basin - transition from turbidite to fluviatile deposition.
6 Monday 1 December 5.30 - 6.30
(cont'd)
Time for viewing poster displays - contributors are asked to be available if p o s s i b l e .
7.30
Dinner
-
Labor C l u b , Belconnen Town Centre.
Tuesday 2 December 9.00 a.m.
David Hilyard, School of Applied G e o l o g y , S.A.I.T.
Mullions Range volcanics
- stratigraphy
and
palaeogeogrphy.
J.W. Pemberton, Department of G e o l o g y , University of Wollongong
The stratigraphy of the volcanic rocks of the Cudgegong District, N.S.W. Mukul R . Bhatia, Geology D e p a r t m e n t , A . N . U .
Rare earth element geochemistry Tasman Geosyncline.
of clastic rocks of the
Morning tea Mike Garratt, G e o l o g i c a l S u r v e y , Victoria
Depositional
model for the Melbourne Trough,
Victoria
£
Business Meeting of A . S . G . t) £
Barbeque lunch K . Corbett
CO
o
Some problems in the Mount Read Volcanics, a Cambrian rhyolite-dacite-andesite complex in Western Tasmania. Peter R . W i l l i a m s , D e p a r t m e n t of M i n e s , Tasmania
Trough sedimentation. fan and base-of-slope Tasmania. £
£ CO
Criteria for distinguishing submarine deposits, Western and South Western
P . J . Conaghan, J . G . J o n e s , K . L . M c D o n n e l l , and K . R o y c e , Macquarie University.
Dynamic fluvial basin model for the Permo-Triassic
Sydney
Basin.
Afternoon tea Chris Fergusson, Geology D e p a r t m e n t , University of New E n g l a n d .
Se dimen to logy of the Late Palaeozoic north-eastern N.S.W.
Coff's Harbour
Beds,
R . J . Korsch, A r m i d a l e C . A . E .
Petrofacies and petrologic evolution of sandstones in Coff's Harbour Block, New England Orogen. J . Fergusson, Geology D e p a r t m e n t , University of New England.
Palaeogeographic significance of Late Carboniferous Pyroclastics, Werrie Syncline, N.S.W. David Lindley, School of A p p l i e d G e o l o g y , University of N . S . W .
Early Carboniferous England Belt. 5.30
sedimentation
in the Southern New
C.O.G.S. meeting, Applied Science Staff R o o m , Building 3 , Floor D .
7 Tuesday 2 December - program additions An ANU Seminar Series on Saline Lakes planned for earlier in 1980 was deferred to link it to the ASG discussions on the same subject and to precede the INQUA Loess Commission Dust Mantle Workshop (Dec. 3-5) involving visitors from China and New Zealand. However, the papers submitted could not be accommodated within the ASG programme without running concurrent sessions at CCAE. To avoid this, the four papers offered will be presented in the Life Sciences Seminar Room (CRES), ANU, on the final afternoon of the ASG meeting, Tues. Dec. 2nd commencing 1:30 p.m. The programme is as follows:
1:30 pm
CLASSIFICATION AND HYDROLOGIC RESPONSE OF SELECTED AUSTRALIAN SALT LAKES Dr J.M. Bowler Dept. of Biogeography & Geomorphology Australian National University
2:00 pm
QUATERNARY DEFLATION OF LAKE EYRE AND DEVELOPMENT OF THE SIMPSON AND TIRARI DESERTS Dr J. Dulhunty Dept. of Geology University of Sydney
3:00 pm
SALT LAKES AS GROUNDWATER DISCHARGE ZONES IN NORTHWESTERN VICTORIA AND NORTHERN CHILE Dr C.R. Lawrence Victorian Dept. of Minerals & Energy Melbourne
3:30 pm
. . . T E A . . .
4:00 pm
HOLOCENE SEDIMENTATION IN LAKE EYRE
4:30 pm
HYDROCHEMICAL AND HYDRODYNAMICAL PROCESSES IN THE SALT LAKE BASINS OF NORTHWESTERN VICTORIA
Dr J. Dulhunty
Mr P.G. Macumber Victorian Dept. of Minerals & Energy Melbourne
8
Wednesday 3 December
Excursions commence.
The following poster displays have been offered : K.A.W. Crook, Dept. of Geology, A.N.U., (1)
Tectonic controls on the distribution in NSW and Victoria.
(2)
Fore -arc evolution
and continental
of Lambian
growth
Fades
- a general
basins model.
Jock Keene, Dept. of Geology, University of Melbourne, Fades
models
for the Mallacoota
Beds.
R.A. Glen, E. Scheibner and D.J. Pogson, Geol. Survey of NSW, Sedimentation
patterns
and trends in the Cobar
Basin.
Brian Jones, Dept. of Geology, University of Wollongong, Lower Devonian
voIconics
at Marulan,
NSW.
JVB* Firman, Evolution
of Palaeosols
in
Australia.
Jan Carey, School of Earth Sciences, Macquarie University, Eolocene
sediments
J.M. Jackson,
BMB's Sedimentary R.V. Burne,
and molluscs
in Sydney
Harbour.
BMR, studies
in the McArthur
Basin.
BMR,
Sedimentology
of Spencer
Gulf.
R.A. Cas, Dept.of Earth Sciences, Monash University, (with C. & J. Fergusson, J.G. Jones, C.McA. Powell, W.D. Roots) The Kowrrrung Volcaniclastics: flow origin3
north-eastern
A deep-water
succession
Lachlan fold belt>
of
mass-
NSW.
Conference headquarters and poster displays will be in Building 3 (Applied Science Building) at the north-east corner of the Canberra CAE campus. Papers will be presented in the Lecture Block, Building 2, immediately south of building 3.
The distribution list for this program is based on applications to attend the ASG conference received by the convenor up to 3 October 1980. CCAE residence accommodation and places on the two field trips are available to all who have applied, to that date.
9 ABSTRACTS INTRODUCTORY COMMENTS
Extended abstracts of the papers to be delivered at the 1980 Conference of the Australasian Sedimentologists Group, Canberra A.C.T. are set out in the order in which they will be given. The abstracts are, for the most part, reprinted exactly as submitted by the authors, and there has been no attempt at stylistic alterations or unification of the abstracts. The papers will be given in lecture room 2B7, Building 2, of the Canberra College of Advanced Education on 1 - 2 December. Also included are abstracts for some of the poster sessions which will be presented during the Conference.
10
QUATERNARY TEMPERATE SHELF SEDIMENTATION
1 December
Convenor:
P. Roy, Geological Survey of N.S.W., Sydney.
XI THE PETROLOGY AND GEOCHEMISTRY OF IRON AND PHOSPHORUS-RICH NODULES FROM THE CONTINENTAL SHELF OF NORTHERN NEW SOUTH WALES
John F Marshall, Bureau of Mineral Resources, Canberra Peter J Cook, Research School of Earth Sciences, Australian National University, Canberra.
Phosphatic-glauconitic-goethitic nodules occur on the continental shelf of northern New South Wales in water depths of about 200-300 m. 1970).
Three types of nodules have been recognised (Von der Borch,
Group A nodules are small (average diameter 3 cm) dull grey,
irregular and unglazed.
They are composed of calcareous skeletal
material, glauconite and goethite pellets, and silt-size quartz grains, in a collophane matrix.
Uranium-series age determinations on this type
of nodule indicate a late Pleistocene age, in the range 50,000 to 55,000 years (Kress & Veeh, 1980).
Group B nodules are compositionally similar
to Group A nodules, but are coated and glazed by goethite and are significantly more iron-rich.
These nodules may be as old as Miocene.
Group
C nodules are conglomeratic cobbles and boulders that are composed of cemented Group B nodules.
At least two stages of apatite precipitation
are evident within the nodules (Marshall & Cook, in press).
Primary stage
apatite consists of well-defined hexagonal plates, 2-3 microns in diameter, whereas the later stage apatite consists of clusters of acicular crystals approximately 1 micron long that are identical to those from recent offshore phosphorites from Chile-Peru (Burnett, 1977).
Whole rock analyses show that the nodules are markedly enriched in Fe 2 0 3 (16.8 to 44.1 percent), but relatively low in P ^ percent).
(5.6 to 11.7
Microprobe analyses reveal that the matrix varies between
essentially pure collophane (29 percent P 2 0 5 ) and goethite (61 percent FeO) (Cook & Marshall in press).
Both glauconite and gpethite pellets within
the nodules are geochemically distinct from the collophane matrix.
The
goethite pellets have probably been produced from the breakdown of glauconite.
If allowances are made for the masking effects of ferruginisa-
tion, then the New South Wales nodules are geochemically similar to other phosphorites that have formed in areas of strong oceanic upwelling, a feature that appears to be mainly absent on the east coast of Australia. The petrological and geochemical interrelationships of the nodule components suggest a rather complex origin that has involved several phases of precipitation, cementation, erosion and transportation, as well
12
as extreme redox fluctuations while the nodules have remained essentially in the marine environment.
REFERENCES
BURNETT, W.C., 1977.
Geochemistry and origin of phosphorite deposits
from off Peru and Chile.
Geological Society of America, Bulletin,
88,813-823. COOK, P.J. & MARSHALL, J.F., in press.
Geochemistry of iron and
phosphorus-rich nodules from the east Australian continental shelf. Marine Geology. KRESS, A.G. & VEEH, H.H., 1980.
Geochemistry and radiometric ages of
phosphat ic nodules from the continental margin of northern New South Wales, Australia.
Marine Geology, 36, 143-157.
MARSHALL, J.F. & COOK, P.J., in press.
Petrology of iron and phosphorus-
rich nodules from the east Australian continental shelf.
Journal
of the Geological Society of London. VON DER BORCH, C.C., 1970.
Phosphatic concretions and nodules from the
upper continental slope northern New South Wales. Geological Society of Australia, 16, 755-759.
Journal of the
13
SALINE LAKE SEDIMENTATION
1 - 2 December
Convenor:
J.M. Bowler, Research School of
Pacific Studies, A.N.U., Canberra
14
CONTINENTAL EVAPORITE FACIES AND THEIR EVOLUTION THROUGH QUATERNARY HYDROLOGIC CYCLES
J.M. Bowler Dept. of Biogeography & Geomorphology Australian National University
The major climatic oscillations that have characterized the last 2 million years have left their legacy within the salt lake systems that often form deposition centres within arid and semi-arid Australian environments.
Not only have such basins responded to past fluctuations
in climate and hydrologic regime
but, more importantly, the key to the
sequence and magnitude of such changes may be preserved in their sedimentary record.
Thus, whilst salt lake sediments constitute an
intriguing study in themselves, they also serve to help establish the age and magnitude of past climatically controlled events.
Data from cores and trenches through a range of lacustrine environments in southern Australia (including L. Mungo, L. Tyrrell and L. Frome) may be summarized in terms of a succession of hydrologic states, a succession which in its simplest form may be presented as a repetition of successive hydrologic cycles ranging through wet-dry-wet oscillations. While most Australian salt lakes exist today in an ephemeral or playa state, this was not always so.
In fact, in terms of the hydrologic status
represented through Quaternary time, the present is the exception rather than the norm.
Typical sedimentary sequences from southern Australian lakes demonstrate a succession of changes, each affected by complex interaction of surface and groundwater components.
In cores analysed from L. Tyrrell
a facies succession is recognised varying from deep to shallow water environments in which the influence of groundwater is at times subordinate to, and at others dominant over,that of surface water.
Assuming a starting point brine with ionic composition approximately equal to that of sea water, a generalized picture emerges, examples of
15
which are represented with cyclic repetition within facies variants of the sediments of L. Tyrrell.
These may be summarised as below.
Table 1: Typical facies variation in salt lake
sedimentary sequences
Deep water, low salinity
Detrital sands, clays with clay fabric showing random orientation. Calcite as encrusting laminae and oncolites.
Decreasing depth, increasing salinity
Increasing carbonate, clay fabric becomes highly oriented.
Sulphate saturation
Deposition of gypsum, prismatic forms. Rhythmic alternation with bands of oriented clay producing laminar banding.
Chloride saturation in very shallow brine
Halite deposition with re-solution during seasonal freshening.
Fall in watertable allows basin floor to dry seasonally remaining within capillary fringe
Capillary efflorescence of sodium sulphate with seasonal deflation producing clay-rich dunes (lunettes)
Further fall in watertable permits downward leaching of salts
Halophytes colonise lake floor with development of pedogenic features on lacustrine sediments.
The identification of these facies in a time controlled sequence, and their relationship to depositional environments enables us to reconstruct the pattern of surface and groundwater fluctuations throughout the last 100,000 years and beyond.
Such fluctuations depict cyclic
oscillations from deep-water environments before 30,000 B.P. culminating in dry dune-building facies between 25 to 15,000 B.P. with the present Holocene regime lying between these two hydrologic extremes.
16
Fig.1
Fig. 2 100 1
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—
-*
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Woods
•
•
/
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40 / / /
2
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10
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^
Fromt • .
/
George
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/// /
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T
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r r
/ c V
^ \ / S : "
4
6
-TyrreLl
10
F. . -Stf • ,
20
40
60
100
17
SALINE LAKES OF THE EYRE PENINSULA, SOUTH AUSTRALIA
P. De D e c k k e r 1 , R.V. B u r n e 2 , J. Bauld 2 , and 2 James Ferguson
1.
Department
2,
Baas Becking Geobiological Laboratory,
of Zoology, University
of Adelaide. Canberra.
The geomorphology, sedimentology, water chemistry,
biology,
and recent history of some Eyre Peninsula saline lakes have been investigated. recognised:
The following geomorphological
Newland); enclosed
bays
playas
(e.g. Pillie Lake); series of
(e.g. Lake Malata); large pans
(e.g. Lake
(e.g. Lake
(e.g. Sleaford Mere); major seeps in
karst depressions near the coast lunettes
types have been
large coastal lakes bounded by dunes
(e.g. Lake Greenly); and
Gilles).
The sediments of the lakes consist mainly of
combinations
of quartz, calcite, aragonite, halite, gypsum, shell and charophyte oogonia. protodolomite
fragments,
There is no evidence of present-day
formation, and protodolomite
subsurface- sediments of Pillie Lake.
is abundant only in
The chemistry of the waters
of the lakes indicate that some are derived
from seawater,
some
from continental groundwaters, and others from mixtures of the two.
Salinities encountered
in November
1979 ranged
from c_a
0.13 x sw up to 8.34 x sw. The lakes have a similar fauna to both those of Yorke Peninsula and those adjacent generally
less diverse.
to the Coorong Lagoon,
though
An exception is a halobiont
of the genus Coxiella which belongs to a Western species not recorded previously
gastropod
Australian
from South Australian
The flora is also similar to that of other coastal
Lakes.
Australian
saline lakes, the halophytes Ruppia and Lep ilaena spp. and
the
charophyte Lamprothamnium papulosum being present in the less saline lakes
(<1.5 x sw).
The filamentous green alga
occurs in several of the lakes. conspicuous
The microflora
in the benthic than the planktonic habitat.
though superficial, blue-green algal observed
Cladophora
is generally
to cover marginal sediments.
bacteria also contribute
more
Coherent,
(cyanobacteria1) mats were Diatoms and
to benthic mat formation.
photosynthetic Lake
contains widespread, thick mats of blue-green algae and
Damascus
18
photosynthetic
bacteria.
Studies of the history of lake
sedimentation have so far been restricted of a short
to a detailed
(^50 cm) core from Pillie Lake.
composition of the fossil ostracod dolomite formed
fauna indicate that
proto-
in the past under conditions of permanent
cover, and at salinities below that of seawater. recorded
analysis
Changes in the
The
water
succession
in the Pillie Lake sediments indicates both a progressive
freshening of the lake water, and an increasing desiccation.
These phenomena may be related
in sea level in the area.
frequency of
to a Holocene
fall
19 SEDIMENTOLOGY AND GEOCHEMISTRY OF A COASTAL ATHALASSIC
SALINE LAKE, SPENCER GULF
L.A. CHAMBERS, JAMES FERGUSON, & R.V. BAAS BECKING GEOB10LOGICAL
BURNE.
LABORATORY
CANBERRA
Lake 19 is an ephemeral lake located at the landward of a regressive shoreline complex on the north-eastern Spencer Gulf, South Australia. which is isolated ridges
It has formed
in a deflation
from the intertidal flats by stranded
(Fig. 1) and which is intermittently
elevation of the water
margin
shore of
flooded by
seasonal
table.
The sediments show a regressive sequence of subtidal, grass-bank
sediments and algal-laminated
are conformably
zone
beach
sea-
intertidal sands.
These
overlain by lake sediments of algal-laminated
sands containing discoidal
mud layer near the surface also containing gypsum.
During
ative phases gypsum and halite may form at the surface. 1977, following a prolonged contained precipitated
fine
gypsum and charophyte oogonia, with a
dry phase, the sediments
evapor-
In May
also
sulphides to a depth coinciding with the
water table level. Although there was no detectable
sulphate
reduction activity at the time of sampling, the sulphur
isotope 34 increasing S
values were typically biogenic, with progressively content
towards the surface.
progressively waters.
depleted
This is consistent with reduction of
sulphate in capillary
zone
interstitial
More recently, sulphate reduction has been
in the topmost
sediments
became established
demonstrated
immediately beneath an algal mat which
after drought-breaking
stantial rise in the water-table
level.
sulphide was oxidised by the rising
rains caused a subMost of the original
groundwaters.
The hydrology of the area is largely controlled by
seasonal
variation of the continental groundwaters, since this also influences the zone, seaward of the lake, in which these i / waters Within Lake 19 the 6 S of
meet and mix with marine brines.
sulphate in solution appears to be representative sulphate
of non-marine
for the region, and gypsum samples show a value only a
few per mil heavier.
This contrasts with gypsum, found
in the
20
b e a c h r i d g e i m m e d i a t e l y s e a w a r d s of t h e l a k e , f o r OA O J 4 6 S = +23.1 / oo*, indicating a seawater sulphate
which
despite
predominantly
the present
groundwater
non-marine.
Farther
distributions
show
an
sulphate's
seawards, both increasing
being
chemistry
marine
origin,
and
isotopic
influence.
o
s vO 0-
+CO
"l ~1 I 1 I—r ' t ! r
to It? ?^ Q
^ e 3
• < • i s/ ms.^'ijs/Z.
§ Q •51 <1 uC £ v qj \ O gists hl|| Kf) Q> lo 5 tf o Ql C Oo o Q- "D *a $I
i ii i £ ii z
1 oo a> <T> £' ~<£o o^ o xj 1® Iis| 8 |S| | R||« ?| | • Ql UO CO I *
a Ul
£ +
* 6 3 4 S ° / O O
=
!(34s/32s)
L
SAMPLE
-
( J 4 S /
S)
o/
32
(
34
S /
32
S)
M E T E Q R 1 T I C
M E T E O R I T I C
10
21
CALCRETES IN SOUTHERN AUSTRALIA
A.R. Milnes CSIRO Division of Soils, Private Bag No. 2, GLEN OSMOND, S. Aust. 5064.
In Australia, in common with many semi-arid countries, there are significant terrestrial accumulations of carbonate in soils and unconsolidated sediments, or on exhumed bedrock surfaces.
They are mainly distributed in
southern Australia in a broad belt flanking the Great Australian Bight and the gulfs region of South Australia, although some occur inland in the central and western parts of the continent and along the western coastline.
These materials
have long been of interest to pedologists and geologists working on Quaternary sediments, but detailed investigations of their relationships and origins are few.
One of the problems has been the lack of an adequate terminology to
encompass the wide variety of forms and relationships such carbonate accumulations display.
Terrestrial carbonate accumulations are not confined to the Quaternary,
but have been recognised in sedimentary sequences as old as Cambrian (Daily 1972) where they are thought to mark unconformities due to subaerial exposure and reworking of calcareous sediments following emergence from a marine environment.
However, in common with many terrestrial deposits, their
preservation may be rarely achieved. Terrestrial carbonate accumulations display a wide variety of forms, as many workers have observed.
Thick, multi-layered profiles overlying unconsol-
idated sediments or bedrock of varying composition and origin characteristically exhibit a surface layer of pisolitic pebbles, cobbles and sometimes boulders, and an underlying consolidated limestone sheet or hardpan which grades downwards through an unconsolidated nodular zone into a mottled to structureless fine earth.
In many cases, a thin soil mantle covers the profiles.
There are
also consolidated and often laminated carbonate-rich crusts on calcareous bedrock, carbonate-filled fractures and joints in the near-surface zones of non-calcareous bedrock, and nodular or mottled carbonate-rich horizons within soil profiles.
Consistent with the suggestions of Goudie (1973) and Netterberg
(1978), the term Mcalcretefl (Lamplugh
1902) has been adopted herein to refer
to the range of carbonate accumulations in the regolith in southern Australia, and more specific adjectival terms (for example pisolitic carbonate, vermicular carbonate, laminated carbonate layer, massive concretionary limestone or hardpan, calcareous fine earth) to describe the various forms.
Read (1974) has
conveniently escaped this potential confusion by using the term flcalcreteM, contrary to Lamplugh's definition, to refer specifically to secondary crypto-
22
crystalline carbonate exclusive of the inherited material in the host, Logan et al. (1970) and Read (1974) regarded the terrestrial carbonate accumulations they studied in the Shark Bay area of Western Australia as variously consolidated calcareous scree and slope deposits and calcareous soils of Pleistocene to Recent age whose form and relationships were highly dependent on the local landscape and topography at the time of their formation.
Although
similar notions had been hinted at by many other authors of papers on calcretes, these appear to be the first attempts to relate the various forms of calcrete to an environment of deposition and consequently a mode of origin.
The current
work (Milnes & Hutton 1980) is more or less an extension of this approach, and is concerned with description of the field relationships and morphology of the various carbonate accumulations in southern Australia, together with collection of geochemical and mineralogical data through selected profiles, in order to establish their origin.
REFERENCES Daily, B. (1972) Aspects of carbonate sedimentation in the Cambrian of South Australia. Abstracts Joint Specialists Groups Meetings, Canberra. Geol. Soc. Aust. C10-14. Goudie, A. (1973) "Duricrusts in tropical and subtropical landscapes." (Clarendon Press: Oxford). Lamplugh, G.W. (1902) Calcrete. Geol. Mag. _9, 575. Logan, B.W., Read, J.F. & Davies, G.R. (1970) History of carbonate sedimentation, Quaternary Epoch, Shark Bay, Western Australia. Amer. Ass. Pet. Geologists Memoir 13, 38-84. Milnes, A.R. & Hutton, J.T. (1980) Calcretes in Australia - a review. In "Soils: an Australian viewpoint". Chapter C4. CSIRO Division of Soils. (CSIRO: Melbourne) (in press). Netterberg, F. (1978) Dating and correlation of calcretes and other pedocretes. Trans. Geol. Soc. S. Afr. 81, 379-391. Read, J.F. (1974) Calcrete deposits and Quaternary sediments, Edel Province, Shark Bay, Western Australia. Amer. Ass. Pet. Geologists Memoir 22, 250-282.
23
SEDIMENTS FROM A CAMBRIAN ALKALINE LAKE, OFFICER BASIN, SOUTH AUSTRALIA YOUNGS B.C., S.A. Oil and Gas Corporation P.O. Box 55, Glenside, S.A. 5065
Pty. Ltd.,
A stratigraphic well, Byilkaoora-1, drilled by the S.A. Department of Mines and Energy in 1979, discovered oil shows in Early Cambrian lacustrine carbonates of the northeastern Officer Basin (Pitt et al., 1980). The well was fully cored and has enabled the depositional history of the lake to be interpreted. Sedimentation commenced with 107m of coarse, piedmont fanglomerate (the "Davies Bore Conglomerate") and was followed by the red and grey-green siltstones and carbonates of the Observatory Hill Beds. These are 224m thick and display a red-grey-red cycle. This lacustrine stage was followed by deposition of the red and white aeolian and fluvial beds of the Trainor Hill Sandstone and Mt. Johns Conglomerate. Four sedimentary features, found primarily within 95m of the central, grey-green carbonates of the Observatory Hill Beds, are of particular interests (i)
abundant calcite pseudomorphs of the evaporite minerals trona, shortite and possible gaylussite occur in fine-grained dolomite mudstones and in close association with algal boundstones.
(ii)
interbedded chert layers and nodules show the concentric colour banding and surface shrinkage cracks typical of Magadi-type non-marine cherts.
24
(iii)
many sedimentary cycles, generally less than one metre thick, are recorded.
Each one,
representing the flooding of the lake area by freshwater and its eventual evaporation, is characterised by evaporitic argillites and dolomite mudstones overlain by algal boundstones with chert layers and breccias. (iv)
oils recovered from vugs and veins demonstrate certain similarities to those associated with the non-marine Green River Formation of the U.S.A. (McKirdy and Kantsler, 1980).
The Observatory Hill Beds in Byilkaoora-1 show many similarities to the Eocene Green River Formation of Wyoming, U.S.A. and are therefore interpreted to have been deposited in a similar highly alkaline playa-lake (White and Youngs, 1980).
The extent of the lake in
the Officer Basin has not been determined but a series of similar tectonically-controlled playas may have covered an area of at least 50,000 square km during the Early Cambrian.
This record of Cambrian alkaline playa-
lake deposition is believed to be the first to be documented in Australia:
many more Proterozoic and Palaeozoic
examples of alkaline lake deposits may be awaiting recognition. McKirdy, D.M. and Kantsler, A.J., 1980. Oil geochemistry and potential source rocks of the Officer Basin, South Australia. Aust. Petrol. Explor. Assoc. Jour.3 20: 68-86. Pitt, G.M., Benbow, M.C. and Youngs B.C., 1980. A review of recent geological work in the Officer Basin, South Australia. Aust. Petrol. Exiplor. Assoc. J our.y 20: 209-220. White, A.H. and Youngs, B.C., 1980. Cambrian alkali playa-lacustrine sequence in the northeastern Officer Basin, South Australia. Jour. Sedim. Pet. 3 50 (4): in press.
25 CLASSIFICATION AND HYDROLQGIC RESPONSE OF SELECTED AUSTRALIAN SALINE LAKES
J.M. Bowler Dept. of Biogeography & Geomorphology Australian National University
In their response to Quaternary climatic and hydrologic fluctuations, no two lake basins will behave in exactly the same manner.
While most will
register a return to wetter conditions if the climate becomes wetter, some will register that change by the development and preservation of high strandline features such as beaches and dunes, together with a diagnostic sedimentary record in the depositional centre, whilst others may not be so affected.
Thus
the response of any saline basin to a sequence of externally induced changes is largely a function of the basin characteristics.
Some will respond
sensitively to change while others may show little or no response.
The sensitivity to hydrologic change of any basin is a function of its local groundwater regime, its catchment/basin area ratio and the climatic regime in which it is located.
For a steady state water balance (assuming
insignificant groundwater flux) the following relationship holds true:
Ac/Al =
E - P -~
+
1
where Ac = area of catchment A1 = basin or water surface area E = mean annual evaporation from free water surface P = mean annual precipitation f = run-off coefficient from catchment to basin.
For a range of Australian lake basins, the relevant parameters have been measured as in Table 1.
These may be represented diagrammatically as in
Fig. 1 (Bowler, in press). Those lakes which plot on the left side of the hydrologic threshold should remain as permanent water bodies while those on the far right, such as Gairdner and Torrens, always remains in the region of groundwater dominance; they seldom if ever cross the threshold for any but short lived seasonal episodes to behave as semi-permanent lakes.
Basins that plot near the threshold are the most sensitive to change. These are the ones most likely to preserve evidence of Quaternary climatic fluctuations.
In several of these we can already identify the existence of
26
Pleistocene shorelines, the dimensions of which enable us to measure the expanded surface area of the water bodies they represent
(Am).
Plotted
on the same axial ratios as Fig. 1, the dimensions of the Pleistocene lakes require a new set of climatic parameters to sustain them (Fig. 2). The magnitude of the changes demonstrated in the history of such basins point to major changes in the climatic regime across Australia, changes that would have been reflected in both surface and groundwater regimes over very large areas.
Bowler, J.M.,
Australian salt lakes: a palaeohydrological approach iji SALT LAKES: PROCEEDINGS OF AN INTERNATIONAL SYMPOSIUM ON ATHALASSIC (INLAND) SALT LAKES, W.D. Williams (ed.) Junk, The Hague. in press.
TABLE 1
. 8E - P Area in Km 2
P
+ 1
f
LAKE BASIN Ac
Am
Ac
P f = 0.1P
P f = 0.3P
Gregory
387
*5492
33,160
44.3
15.4
Woods
423
5476
25,300
34.0
12.3
Eyre
9400
NA
1,316,000
216.0
58.1
Gairdner
4520
-
11,180
119.0
40.3
Torrens
5640
-
27,000
119.4
40.3
Frome
2550
*3100
24,500
100.7
34.0
Tyrrell
155
* 258
**647
22.7
7.6
Galilee
260
5000
22.7
7.6
Buchanan
115
3110
22.7
7.6
Keilambete
2.77
4.17
1.64
1.21
L. George
155
321
950
*
Minimum figure, ancient shoreline
**
Lake Tyrrell is fed by an overflow channel from the Avoca River. Its effective catchment, difficult to define, is taken as h x Avoca catchment
partly obscured.
27 QUATERNARY DEFLATION OF LAKE EYRE AND DEVELOPMENT OF THE SIMPSON AND TIRARI DESERTS John A. Dulhunty Department of Geology and Geophysics University of Sydney
Geological and geographical studies have revealed some of the geomorphological history of Lake Eyre and surrounding country.
However,
many problems still remain in relation to the number and sequence of events which have contributed to the development of landforms and physical environments as they are today. There is good evidence of the existence, probably throughout most of Pleistocene time, of a freshwater lake called Lake Dieri which occupied the present position of Lake Eyre, and extended beyond in most places.
It seems that Central Australia then enjoyed a reasonably high-
rainfall climate, and large rivers rising in the Northern Territory and northwestern and western Queensland flowed south and west into Lake Dieri which overflowed, through the Torrens Rift and Spencer Gulf, to the Southern Ocean. Late in Pleistocene time, possibly between 30 000 and 40 000 years ago, rainfall commenced to diminish; evaporation increased, and Lake Dieri no longer overflowed.
Aridity gradually increased until the
lake was dry, and in early Holocene time, perhaps 10 000 years ago, a maximum degree of aridity was reached.
This was either the peak of a long
arid cycle, or more likely a high on a profile over rising peaks of shorter arid cycles.
At the time this maximum was reached, no doubt as
a result of aridity rather than associated tectonism, the water table fell to about 20 m below the surface of the unconsolidated Pleistocene freshwater Lake Dieri sediments.
This allowed deflation of the lake bed by some 20 m,
28
during which fine material was carried away by wind and sand migrated generally to the northeast, possibly filling in some northeastern areas of the original lake.
High shoreline dunes were formed along the
northern, northeastern and eastern sides of the main deflated area, which then became Lake Eyre. The shoreline dune system extended back some distance from the margin of deflation, and sand carried across the dunes commenced to accumulate in arid areas to form the sands of the Simpson and Tirari Deserts.
Later in Holocene time, perhaps some 7 000 years ago, aridity
seems to have decreased to some extent; rainfall increased, and the water table commenced to rise.
Rivers from the Northern Territory and Queensland
carried floodwaters south through the deserts, occasionally reaching Lake Eyre to evaporate and make the arid terminal lake a playa-salina.
During
flooding the rivers carried new sand from their elevated northern headwaters, and deposited it along wide desert channels and in deltas where they entered the lake.
This sand was blown out from deltas and channels, and added to
the earlier sands of deflation. The prevailing winds which caused the early deflation of Lake Eyre, seem to have varied from westerlies to southerlies, moving sand generally from southwest to northeast.
Later they varied between south-
westerlies and southeasterlies, moving sand from south to north along longitudinal ridges, as at present. The rise in water table, following the main deflation of Lake Eyre, must have been due, partly at least, to increased rainfall, and possibly also to subsidence of the lake area.
It has now risen by some
6 m which, with intermittent flooding of the lake, has resulted in accumulation of about 6 m
of Holocene sediments.
This has prevented
further deflation of the lake bed, and the old shoreline dunes lacking adequate source material are now undergoing erosion, and their sand, together with new river delta and channel sand, is carried over their remnants onto the longitudinal ridges of the Simpson and Tirari Deserts.
29
SALT LAKES AS GROUNDWATER DISCHARGE SYSTEMS IN NORTHERN VICTORIA AND NORTHERN CHILE by C.R. Lawrence Victorian Department of Minerals and Energy
For the semi-arid to arid areas of the central Murray Basin and the Atacama Desert there are salt lakes and associated evaporite deposits in the topographic lows which represent completely or partly closed groundwater discharge points.
The salinas of the Murray Basin are characterized by thin deposits of halite and gypsum.
A "first-up" mathematical model of two-dimensional steady-state type
indicates the quantitative relationship to the regional groundwater flow system in the general sense.
The complexities, not represented in this simple model,
are discussed in the paper by P.G. Macumber.
By contrast to the salt lake of the Murray Basin, those of the Atacama Desert are in a region where rainfall is virtually negligible where there is far greater topographic relief, which is still technically active with associated volcanism, and where extensive alluvial fans are prevalent.
A series of extensive salinas
occur immediately westward and within the Andes Ranges, including the Salar de Ascotan, Salar de Carcote, Salar de Atacama, and the Salar de Punta Negra. Beneath each salina are thick (up to 1000 m) bodies of halite, saturated with a brine enriched in lithium, and surrounded by gypsum and the boron mineral, ulexite. The brine extends beneath the adjoining alluvial fans and has a very gently inclined interface with the overlying fresh groundwater.
For most salinas, benches capped
with calcrete are preserved up to several hundred metres above the lake floor.
In contrast to these salinas are the less well-defined and extensive areas of sodium and potassium nitrate deposits which exist in the topographic low, known as the Pampa of Tamarugal and located between the Andes and the Coastal Range. These sites are interpreted as being precipitated by capillary action from a shallow water table.
Apart from these two forms of evaporite deposition, because of the extremely dry conditions there is a large variety of salts found also in other situations.
30
HOLOCENE SEDIMENTATION IN LAKE EYRE John A . Dulhunty Department of Geology and Geophysics University of Sydney
Lake Eyre is an outstanding geomorphological phenomenon with a unique diversity of sedimentation, erosional and physical environments. It forms the arid terminal sump of
one of the world's largest internal
drainage basins, covering almost one sixth of the total area of the Australian continent.
It is situated in the most arid place in Australia
with an average annual rainfall of less than 150 m m .
It is also the lowest
place in Australia, with its bed wholly below sea level, falling to about -15 m (Australian Height Datum) at several places in Lake Eyre North. 2
The lake consists of two parts, Lake Eyre North (8030 km ) and 2
Lake Eyre South (1300 km ), connected by the Goyder Channel through which water flows only during deep floodings.
The bed of Lake Eyre North slopes
gently, at 3.75 cm per k m , from the northern and northeastern shores, where rivers from the Northern Territory and Queensland enter, to the lowest places in the southern bays. southern shoreline.
It then rises again at 7 cm per km, to the
Salt crusts, up to 46 cm thick, overlie watery silt,
up to 6 m deep, in low areas of the southern bays, where the final evaporation of brines takes place.
In the northern two thirds of Lake Eyre North, the
surface is occupied by silt at least 3.1 m deep, without salt crust. The lake is surrounded by arid lands: the sandy Simpson and Tirari Deserts to the north and east, and mainly stony desert areas to the west and south.
Floodwaters from monsoon rains in the north, flowing through
desert channels, frequently reach the lake in small quantities, and occasionally as large floods which cover the lake bed to depths of 6 m and more, forming a temporary ocean of water in the most arid place in the country.
As the lake forms a geodetic sump, groundwater in the internal
31
drainage basin moves towards it, and the water table tends to coincide with the lake bed. During an early Holocene period of extreme aridity, little or no river water appears to have reached the lake, and deflation of its bed proceeded as the level of the water table gradually fell through some 20 m. Then with subsequent decrease in aridity, increase in rainfall, and rise in water table, sediments were introduced by intermittent flooding of rivers, as they are today. During mid and late Holocene time, the tilting of Lake Eyre North to the south has developed two different arid lacustrine sedimentary environments:
(i)
arid terminal playa sedimentation in the northern
two thirds from which water drains to low places in the south, and (ii)
arid terminal salina sedimentation in the southern one third where
final evaporation leaves salt crusts.
(i)
In the northern environment, water drains off and evaporates between
floodings, and where introduced sediments have built up above the upper limit of capillarity from the water table, that portion which dries is blown out of the lake.
However, where the sediments are within the zone
of capillarity, and remain moist, they are retained and become part of the Holocene sediments.
So sedimentation in this environment is controlled
mainly by the level of the water table, which in turn depends on rainfall over the basin and subsidence or other tectonism in the lake area.
(ii)
In the southern environment, introduced sediments are protected by a
salt crust from wind erosion between floodings.
When fresh floodwater
carrying fine clay silt, covers the salina to a depth exceeding half the maximum wavelength of surface wind waves, it becomes saline by solution of some salt which aggregates and precipitates suspended clay silt on to the surface of the remaining crust.
Absence of surface wave agitation then
32
allows a thin brine layer to form over the surface of the residual crust. This prevents further solution until the lake water evaporates down to less than half of the surface wavelength, when the brine layer is disturbed and mixes with the overlying saline water.
The remaining
crust is then dissolved, and the aggregated silt, together with organic matter added in the interim and now under attack by sulphur bacteria, falls to lie on the surface of old underlying silt.
Finally the saline
floodwater evaporates, salt crystallises, and a new crust is developed on top of the new silt.
33 HYDROCHEMICAL A N D HYDRODYNAMICAL PROCESSES IN THE SALT LAKE BASINS OF N . W . VICTORIA P . G . M a c u m b e r , V i c t o r i a n D e p t . of Minerals & Energy Melbourne, Vic. In northern Victoria there is a strong interaction b e t w e e n the groundwater systems and surface systems each of w h i c h makes up an aspect of a single down-basin flow s y s t e m .
In the aeolian
Mallee landscape of N . W . V i c t o r i a , surface drainage is virtually a b s e n t , and downbasin flow is essentially via the groundwater s y s t e m s , the uppermost of w h i c h is developed in the unconfined late Tertiary Parilla Sand a q u i f e r .
O n passing down-basin the
w a t e r table gradually approaches the surface to become artesian i n the northern Mallee w h e r e groundwater outcrop is evidenced by the m a n y scattered saline lakes and gypsum f l a t s , and by the very large groundwater discharge complexes - the boinkas (Macumber in p r e s s ) . A p a r t from the groundwater d i s c h a r g e , w a t e r w i t h i n the M a l l e e salt lakes is also derived from direct precipitation and l o c a l run-off.
The dissolved salts are h o w e v e r essentially of
groundwater o r i g i n , and the chemistry of the lakes closely reflects that of the r e g i o n a l Parilla Sand a q u i f e r .
Nevertheless,
distinct g e o c h e m i c a l provinces have developed w i t h i n both the lake systems and the aquifers underlying the lakes.
The m a j o r
processes governing the provinciality are twofold - the d i f f e r e n t i a l evaporitic concentration of salts w i t h i n the l a k e s , followed by their reflux into the underlying a q u i f e r s . distinct types of reflux action can be s e e n . of the refluxed brines
Two
The high density
(at Lake T y r r e l l the density is 1.160)
promotes underflow from the lake b e n e a t h the less dense r e g i o n a l groundwaters
(S.G. 1 . 0 4 ) , as the hydrostatic
equilibrium
34
between the lake and the groundwater system is pushed further in the direction favouring reflux processes. The character of the geochemical provinces provides an insight not only into the major chemical processes active in the salt lakes, but also into the hydrodynamics of lake groundwater interactions, both now and in the past.
Differences
between refluxed waters and their present day salt lake equivalents suggests that a significant change in lake hydrology occured within the last millenium.
35
EPEIRIC SEA SEDIMENTATION 1 December Convenor B.M. Radke, Bureau of Mineral Resources, Canberra.
36
LATE PROTEROZOIC MAGNESITE SEDIMENTATION AN EPIRIC SEA OR SALINE LAKE IN SOUTH AUSTRALIA?
Burton Murrell CRAE Pty. Ltd. ABSTRACT The level of erosion in the Willouran Ranges has exposed sections through the Burra Group across a wide area, allowing a three-dimensional picture of the depositional basin to be built up. The stratigraphic succession is divided into a lower dominantly clastic unit (Copley Subgroup), a middle carbonate-rich unit (Mundallio Subgroup) and an upper clastic unit (Bungarider Subgroup). The Burra Group basin was elongate north-west to south-east and the basin margins to the south-west and north-east marked by clastic wedges during the Copley Subgroup clastic sedimentation. The deposition of sedimentary magnesite with dolomites and limestones along the south-western side of the basin within the Mundallio Subgroup is concluded to be the key to the basin chemistry as a whole. The origin of the sedimentary magnesite is discussed in terms of earlier views on Adelaide Geosyncline deposits, other sedimentary magnesite deposits, possible chemical mechanisms and the models of Strakhov and of Muller, Irion and Forstner for magnesian carbonate deposition in non-oceanic marine basins and lakes. Models of the Burra Group basins are proposed.
37
MODELS FOR CYCLIC SEDIMENTATION IN EPEIRIC CARBONATES OP THE GEORGINA BASIN
B.M. Radke, Bureau of Mineral Resources, Canberra
In many of the carbonates from the Middle Cambrian to Lower Ordovician sequence of the Georgina Basin, shallowing-upward sequences can be recognized. Transgressive-regressive cycles have been described for shallow-water marine carbonates of most ages, and models for explaining this cyclicity have invoked a variety of mechanisms which include:
sea-level fluctuations caused
by episodic tectonism, glaciations, climatic rhythmns, or variable sea-floor spreading rates; processes.
and internal self-guided and regulated 'carbonate factory1
Shallowing-upward sequences in the Georgina Basin indicate cyclical
short term events, geologically speaking, and record the environmental changes within this event.
The generalised cycle, usually less than 5 metres thick, overlies a lower erosional surface of minor relief, with a basal flat-pebble conglomerate lag deposit, followed by a fining-upward sequence with increasing features of high salinity and emergence, to an upper erosional surface with variable induration and phosphatisation.
This sequence reflects a change with
progradational shoaling, from initially lower salinity and higher energy condit ions, through increasing salinity and decreasing energy, to evaporitic and emergent conditions.
This trend is superimposed on initially variable salinity and energy conditions.
These variations have created a diversity of sediment types which
are categorized into SO (skeletal-ooid carbonate) cycles, P (peloid carbonate) cycles, and A (cryptalgal) cycles.
Skeletal-dominant sediments accumulated
under normal-marine conditions, while cryptalgal and peloidal sediments were dominant in higher salinities.
In higher energy conditions, pebble-conglom-
erates and domed stromatolites were more abundant.
The absence of
transgressive components in the cycles implies a non-depositional transgressive event.
In comparison to the duration of deposition of one cycle,
isostatic and eustatic sea-level rises were negligible in their effect, although eustatic drops did initiate emergence and erosion.
38
Platform slope had significant influence on the style of cyclicity.
Where low gradients existed with significant tidal effects, the
'carbonate factory model* of self-guided and regulated production and deposition is applicable.
This required relatively stable eustasy and
produced skeletal-ooid (SO) cycles in a prograding linear belt paralleling the shoreline.
Where slope was negligible, scattered shoals coalesced by lateral accretion in a regional patchwork pattern.
Tidal influence was reduced to
insignificance, and energy and salinity conditions were more variable regionally as well as locally over each shoal.
These variations accounted
for a greater diversity in sediment type and a closer association of P and A cycles.
39 FINE GRAINED CLASTIC SEDIMENTATION IN AN EPEIRIC SEAA MODEL FROM THE CAMBRIAN OF SOUTH AUSTRALIA P.S. Moore, Delhi Petroleum,Adelaide The Nildottie Siltstone Member (Moore, 1979a, 1979b, 1980) is the middle member of the Billy Creek Formation in the central and northern Flinders Ranges, South Australia.
It consists of red shale and siltstone, with minor fine-grained
sandstone and represents deposition mainly in the paralic zone of an epeiric sea. Five facies are recognised and a model of deposition is presented on this basis (Fig. 1).
A general lack of cyclicity in the sequence suggests that there was a
delicate balance between subsidence and sedimentation.
The considerable lateral
extent and thickness of the paralic facies suggests that the palaeoslope was very low and epeiric conditions pertained.
A lack of coarse detritus in the sequence
is further evidence for an extremely low amplitude, senile topography, with sediment supply by sluggish, low competence streams.
Thus, an extensive muddy-
alluvial flood plain probably flanked a broad zone of intertidal sediments. Intertidal and shallow subtidal, tide-influenced deposits constitute the bulk of the sequence.
Evidence for tidal activity occurs in the intimate
association of wave, current, flat-topped and interference ripples, desiccation cracks, mudflake breccias, halite casts, marine trace fossils and raindrop imprints.
In addition, poorly defined wavy and lenticular bedding occur, which are
identical to bedding structures in Recent, fine-grained tidal deposits (Thompson, 1968).
The consistent bipolar orientation of ripple marks favours a low energy
tidal origin for these sediments, with crests aligned subparallel to the coastline and currents directed on and off shore. The tidal range during deposition is unknown, since there are no palaeotidal range sequences.
However, the relative abundance of wave-formed ripples (commonly
with desiccation cracks) suggests that tidal currents were relatively weak.
The
poor sorting of the sediment and a general lack of tidal channels are further evidence of weak tidal flux.
In addition, modern studies of muddy intertidal
environments (Thompson, 1968) suggests that channel development is inhibited by a lack of coarse-grained detritus.
Thus, in the absence of barrier sands, tidal
waters move over the flats as broad, uniform flows.
Ebb currents also flow
across the tidal flats, instead of draining into tidal gullies, thus promoting the development of mudflake intraclasts and ebb-flow ripple orientation. River flood-plain deposits have not been positively identified, although it is acknowledged that the 'transitional environment1 continental in origin.
(Fig. 1) is, in part,
The red colour of the sediment in the Nildottie Siltstone
Member does not necessarily imply continental deposition, since it may have originated in a marginal marine environment where salinity was sufficiently high to prevent the activity of sulphate-reducing bacteria.
MOORE, P.S., 1979a:
Stratigraphy and sedimentology of the Billy Creek Formation
(Cambrian, Flinders Ranges) and its equivalents on the northeast coast of
40
Kangaroo Island, South Australia.
(unpub. Ph.D. thesis) University of
Adelaide, S. Aust. MOORE, P.S., 1979b:
Stratigraphy and depositional environments of the Billy
Creek Formation
(Cambrian), central and northern Flinders Ranges, South
Australia.
Trans. R. Soc. S. Aust., 103, 197-211.
MOORE, P.S., 1980:
Stratigraphy and depositional environments of the Billy
Creek Formation
(Cambrian) east of the Flinders Ranges, South Australia.
Trans. R. Soc. S. Aust., 104. THOMPSON, R.W., 1968:
Tidal flat sedimentation of the Colorado River delta,
northwest Gulf of California.
Figure Is
Geol. Soc. America Mem. 107.
Depositional model for the Nildottie Siltstone Member - a fine-grained, redbed-clastic, epeiric sea sequence.
shaly siltstone
j ,
I Desiccation Halite
cracks
Wave
' / / / / / / / / / X Z Z L z z a
anhydrite
>
ripples
Current
////
v z z z z z z z z ? ^ ?
ripples
Interference
ripples
Flat - topped
ripples
Mudflake
EZZZZZZZZZZ2ZZZZ3 T Z Z Z Z Z Z Z Z Z Z z z z m / / / /A
intraclasts
thickness
Flaser
J silty | shale
i
imprints
Gypsum -
Bed
siltstone & very f i n e sandstone
/ / / / / / 7 T T
bedding
Wavy
bedding
Well
laminated
mudstone
(shale)
Biocky
mudstone
Sorting
and
maturity
t z z z % Z Z 2 Z Z Z Z Z £ t t z z z ^ z z i //
2 / /t
TZ t/
Z2. Z2L 7 Z Z Z Z 2 Z Z 2 Z
v z z z Z & Z Z Z z z z z *
41
TASMAN GEOSYNCLINE SEDIMENTATION
1 - 2 December
Convenor R. Cas, Dept. of Earth Sciences, Monash University Clayton, Vic.
42
FORE-ARC MODELS AND PHANEROZOIC FLYSCH: FALLACY OR FUNDAMENTAL INSIGHT? Keith A.W. Crook Department of Geology, Australian National University, Canberra, 2600 Most workers attribute the extensive flysch terrains of New England, NSW1 and the Rangitata Orogen of New Zealand2 to sedimentation associated with active ocean margins, where subduction was taking place. Earlier attempts to explain the flysch terrains of the Lachlan Fold Belt in terms of active margin evolution
and the development of
marginal seas have failed to achieve a consensus3. Studies of modern fore-arc regions in the Aleutians1*, Makran (Iran)5, Sumatra6, Mexico7 and Barbados8 have demonstrated the importance of flysch and pelagic sediments in both the fore-arc basins and the subduction complexes that constitute the accretionary prisms or wedges which grow outwards from the volcanic arcs. Models9 based upon modern fore-arcs have been elaborated10»11 and used to interpret the Mesozoic in California10 and the Paleozoic of the Southern Uplands, Scotland12, a concensus being reached in each case.
Somewhat similar interpretations of the Lachlan Fold Belt 13
and the Phanerozoic of New Zealandli+ remain controversial, at least in part. Although the ultimate relevance of fore-arc models is far from established, some preliminary conclusions can be drawn: 1.
The post-subduction history of fore-arc regions is important. It can be assessed both by retrospection based on ancient rock 1 q
sequences10, and by actualism based on fore-arcs where subduction ceased during the Cenozoic, e.g. in the northern Andaman arc 15 , Palawan16 and Puerto Rico17. 2.
Fore-arc evolution may be an important mechanism for incorporating
3.
Criteria for discriminating between fore-arc and alternative
flysch into continental crust.
explanations of flysch terrains are few, and not particularly robust.
Petrography provides some control.
The structural
state of the materials (presence of melange) may help. However the Southern Uplands show that flysch in a subduction complex may be very weakly deformed indeed. Presently the most fruitful course lies in careful study of the stratigraphic and structural relations between flysch and other units, using a range of working hypotheses about the possible nature of
43
relationships, guided overall by a fore-arc model.
However, in the absence
of more robust criteria, acceptance of interpretations based upon fore-arc models depends ultimately on the degree of coherence imparted by the interpretations.
Some indication of the lattitude inherent in
such an approach is provided by alternative fore-arc-based interpretations of the Maneroo Terrain of SE NSW and east Gippsland.
A definitive test
for the validity or falsity of such interpretations has yet to be devised. 1. 2.
3.
4. 5.
6. 7. 8. 9.
10. 11. 12. 13. 14. 15. 16. 17.
Scheibner, E. 1973. J. geol. Soc. Aust. 20, 405-426; Leitch, E.C. Bull. geol. Soc. Am. 86, 141-144; Landis, C.A. & Bishop, D.G. 1972. Bull. geol. Soo. Am. 83, 2267-2284; Coombs, D.S. et al. 1976 Am. J. Soi. 276, 561-603; Carter, R.M. et al. 1978 in Stanley, D.J. & Kelling, G. (eds) Sedimentation in submarine canyons, fans and trenches, DH & R Stroudsberg, PA, 340-361. Packham, G.H. & Leitch, E.S. 1974 in Denmead A.K. et al. (eds) The Tasman Geosyncline, a symposium, 129-156, Geol. Soc. Aust. Qd. Div., Brisbane; Rutland, R.W.R. 1976. Earth-Sci. Rev. 12, 161-196. Moore, J.C. 1973. Bull. geol. Soc. Am. 84, 2005-2020; Von Huene, R. 1979. Am. Assoc. Petrol. Geol. Mem. 29, 261-272. Fakhoudi, G. & Karig, D.E. 1977. Geology, 5, 664-668; McCall, G.J.H. 1980. Abs. Brit. Sedimentol. Res. Gp. Symp. London, 21-22; White, R.S. 1980. idem., 42. Karig, D.E. et al. 1979. Am. Assoc. Pet rol. Geol. Mem. 29, 223-237. Moore, J.C. et al. 1979. Nature, 281, 638-642. Pudsey, C.J. & Reading, H.G. 1980. Abs. Brit. Sedimentol. Res. Gp. Symp. London, 30-31; Westbrook, G.K. 1980. idem., 40-41. Seely et al. 1974. in Burk, C.A. & Drake, C.L. The geology of continental margins. Springer, N.Y., 249-260; Karig, D.E. & Sharman, G.F., 1974, Bull. geol. Soc. Am. 86, 377-389. Dickinson, W.R. & Seely, D.R. 1979. Bull. Am. Assoc. Petrol. Geol. 63, 2-31; Crook, K.A.W. 1980. J. struct. Geol. in press. Leggett, J.K. et al. 1979. J. geol. Soc. Lond. 136, 755-770. Crook, K.A.W. 1980. J. geol. Soc. Aust., in press. Crook, K.A.W. & Feary, D.A. 1980. Tectonophysics in press. Curray, J.R. et al. 1978, Am. Assoc. Petrol. Geol. Mem. 29, 189-198. Hamilton, W. 1977. Am. Geophys. Un. Maurice Ewing Ser. 1, 15-32. Perfit, M. et al. 1980. Mar. Geol. 34, 125-156.
44
THE
PALAEOGEOGRAPHIC
SOUTHEASTERN
EVOLUTION
AUSTRALIA
AND
OF
THE
CONSTRAINTS
PALAEOZOIC ON
THE
LACHLAN
CHOICE
OF
FOLD
BELT
OF
TECTONIC
MODELS
RAY CAS
Department of Earth Sciences, Monash University, Clayton, Victoria, 3168.
The distribution patterns of lithological sedimentary facies in the Lachlan Fold Belt changed markedly from the Cambrian through to the Late Devonian-Early Carboniferous.
The Cambrian to Early Silurian time interval was dominated by
sedimentary facies of deep-water affinity.
Shallow marine sequences were
confined to the southern and western margins of the fold belt, adjacent to the stable continental margin, and, in association with isolated piles of mafic volcanics, which were island volcanoes located within the fold belt.
The mid-
Silurian to Early Devonian time interval was characterized by localized areas of deep-water sediments and in some instances volcanics, separated by shallow marine limestones, terrigenous epiclastics and volcanics, some subaqueous, some subaerial.
The volcanics were overwhelmingly silicic and were accompanied by
contemporaneous granitoid plutonism.
Extensive tracts of fluvial-alluvial
sediments are rare but became more prominent in the late Early Devonian in the western part of the belt.
The Late Devonian-Early Carboniferous time interval
was dominated by fluvial-alluvial sedimentation.
In the eastern half of the
belt limited shallow marine incursions occurred and bimodal suites of volcanics are common near the bases of these successions.
Minor granitoid plutonism
also occurred.
Modern palaeogeographic analogues for these are (a) Late Ordovician: Nicobar Basin, arc and adjacent borderlands; the Indonesian archipelago;
(c) Late Devonian-Early Carboniferous:
Range Province of the western United States.
Andaman-
(b) Mid-Silurian-Early Devonian: Basin and
The Cambrian system is poorly
understood and no modern regional, palaeogeographic or tectonic analogue is ventured.
The status of the Andaman-Nicobar system as a tectonic analogue for the Lachlan Fold Belt during the Ordovician remains uncertain because the nature of the basement at that time (and before) remains uncertain.
Secondly, a subduction
complex associated with the Ordovician arc has not been identified.
Although
the Ordovician flyschoid sequences along the preserved eastern half of the belt are complexly deformed, it has not been demonstrated that they have the structural style commonly identified with subduction complexes.
Furthermore
45 the timing of deformational events is poorly understood.
The Indonesian
archipelago is probably a good tectonic analogue for the Siluro-Devonian. Both are partly submerged magmatic arcs founded upon a sialic or continentaltype crust.
Although an unequivocal subduction complex has not been identified
for the Lachlan Fold Belt, complexly deformed flyschoid sediments lie in a suitable position in the New England Fold Belt to the northeast.
The Basin and
Range analogue is probably also a good tectonic analogue for the Late DevonianEarly Carboniferous although on present information the area in southeastern Australia which experienced rifting, bimodal volcanism and the formation of graben-controlled sedimentary basins was much narrower and more restricted than for the modern analogue.
The progressive changes in facies distribution patterns throughout the history of the Lachlan Fold Belt were documented by choosing 14 successive time slices ranging from about 5 to 25 m.yrs, each in duration.
Analysis shows that from
the Late Ordovician (at least) to the Late Devonian-Early Carboniferous, deepwater environments became progressively less prominent relative to shallowmarine and terrestrial environments, although rates of emergence at various stages may have varied.
This time-span includes the several orogenies that
have traditionally been accepted as affecting the belt.
None seem to have
succeeded in producing a regionally extensive, subaerial mountain range or orogen, or in stabilizing the belt for any significant time.
It seems more
realistic to attribute the orogenic history of the belt to one orogeny, the Lachlan Orogeny, which is characterized by several regionally localized deformational events, contemporaneous sedimentation and magmatism, as suggested by C. McA. Powell of Macquarie University.
In modern orogens orogenic
activity marked by contemporaneous deformation, sedimentation and magmatism span long periods of time rather than short, sharp, discrete intervals.
46
THE GROWING LACHLAN OROGEN REFLECTED IN SEDIMENTS OF THE NORTHERN LACHLAN FOLD BELT
C.McA. POWELL, School of Earth Sciences, Macquarie University North Ryde, N.S.W. 2113
The Ordovician to Carboniferous history of the Lachlan Fold Belt can be considered in terms of two major palaeogeographic configurations:
An
Ordovician to earliest Silurian island-arc and marginal-sea province analogous to the modern Andaman Basin, followed by a Basin-and-Range-style province of horsts and grabens in the eastern Lachlan Fold Belt with a foreland basin to the west.
The second palaeogeographic configuration began in mid-Silurian
and lasted until mid-Devonian, after which a sheet-like continental red-bed succession spread across most of the fold belt. The mid-Silurian to mid-Devonian palaeogeographic configuration is synchronous with the growth of the Lachlan Orogen, which was centred in southeastern NSW and eastern Victoria and characterized by silicic magmatism and local episodic deformation from 430 Ma to 380 Ma.
The growth of the
Lachlan Orogen has features analogous to the development of a diapir, with the Basin-and-Range rift province lying above the zone of upwelling, and the flanking foreland basin reflecting the complementary synclinal rim.
Regional
subsidence accompanying cooling of the silicic magmatic core of the orogen from mid-Devonian onwards allowed the flanking foreland basin to retrogress over the horst and graben terrain and pass upwards into a sheet-like continental red-bed succession.
The onset of Early Carboniferous deformation in
the northeastern part of the fold belt generated conglomerates from the newly-deposited marine Lambie Facies.
47
DEVONIAN SEDIMENTS IN THE COBAR BASIN:
TRANSITION FROM TURBIDITE TO
LITTORAL DEPOSITION, R.A. Glen,
Geological Survey of N.S.W.
Box 5288.
G.P.O.
Sydney.
The Cobar Basin is one of a series of marine basins and troughs which developed in central western and western N.S.W. in the Latest Silurian and Early Devonian.
The eastern margin of the Cobar Basin was probably fault
controlled and is now defined by a zone of north to northwest trending reverse faults.
The western margin is less well known:
in the SW corner
of the basin it is defined by a line ot basement granite highs. The Cobar Basin is dominated by a 7-8 km thick sequence of Latest Silurian to late Early Devonian turbidites.
Four distributary systems
have been identified to date on the basis of sparse palaeocurrent. data, sandstone composition, and thickness variations of key marker units.
The
first system was derived from the eastern margin of the basin, with sediment transport/dispersal in a southwest to south direction.
Lithofacies vary
from pebbly sandstone through massive sandstone + interbedded siltstone to thin sandstone + interbedded siltstone and laminated siltstone.
(classical thin-bedded turbidite)
A general fining-up character reflects retro-
gradation of a small turbidite wedge (? fan) which developed immediately after basin, formation.
The second system, in the northernmost part of
the basin is a large south to southeast oriented distributary system. Lithofacies include siltstone, interbedded siltstone and sandstone (classical thin-bedded turbidite) and massive sandstone.
The third system,
in the southern part of the basin, is a large north to northwest oriented distributary system.
Lithofacies vary from sandstone through classical
thin-bedded turbidite to siltstone. than in the second system.
Lithic f ;agments are more common here
The fourth distinct system of unknown size is
situated towards the south western margin of the basin with sediment dispersal in a east to northeast direction.
These last three systems all
show coarsening-up, thickening-up sequences in their lower parts (from siltstone to massive sandstone), followed in their upper parts by fining-up, thinning-up trends from massive sandstone to classical thin-bedded turbidite. Based on the northernmost system, these three systems are interpreted as reflecting progradation followed by retrogradation of submarine fans with lenticular massive sandstones representing depositional lobes (with minor channeling) in the outer middle part of submarine fans.
48
Turbidite sequences towards the western side of the Cobar Basin are overlain by shelf sediments 2-2.5 km thick. here are:
Three lithofacies present
1) a lower fossiliferous, thickbedded sequence of siltstone and
sandstone (the latter characterised by planar and cross bedding and
by
? hummocky
cross
stratification);
2)
a middle sequence
of thick siltstone and thin sandstone (the latter characterised by planar lamination);
3) an upper thickbedded sequence of siltstone and planar and
cross bedded stratified sandstone.
The latter contains Skolithos
burrows and wuttagoonaspid fragments.
This shelf sequence is interpreted
as grading from a "deeper11 water environment in which sandstones were generated by storm-type processes to a neritic and littoral (locally brackish) environment. Marine deposition in the Cobar Basin ended in the late Early Devonian and at least the western part of the basin became the site of deposition from a prograding fluviatile system.
The boundary between the marine and
fluviatile systems varies from locally angular unconformable through disconformable to conformable.
The lower part of the fluviatile sequence
forms an upward fining cycle from sandstone and pebbly sandstone (channel + ? bar deposits in a low sinuosity stream) to sandstone and siltstone (point bar deposits in a higher sinuosity stream).
This sequence is
superseded by the main bulk of fluviatile sediments which consists of cycles of sandstone, pebbly sandstone and siltstone deposited in streams of variable sinuosity.
49
MULLIONS RANGE VOLCANICS - STRATIGRAPHY AND PALAEOGEOGRAPHY David Hilyard, South Australian Institute of Technology. The Middle Silurian Mullions Range Volcanics in the Mullion Creek-Kerrs Creek area of New South Wales (figure 1), consist of rhyolite and dacite lavas and intraformational sediments, lying on the eastern flank of the Molong Rise. Two members can be recognized:
the lower member, A, consists of very
fine-grained, quartzophyric lavas interbedded with volcanic-lithic breccias, quartz-rich lithic sandstones, and siltstones.
The upper member, B, consists
of fine-grained feldsparphyric lavas and quartzofeldspathic sandstones. Traced northwards, the members become thinner and lavas and coarse-grained sediments decrease in abundance.
Lavas show flowbanding, autobrecciation, columnar jointing, and vesicles. Individual flows are not laterally continuous.
They consist of quartz and
albite phenocrysts in a fine-grained, originally glassy groundmass. The clastic rocks are laterally discontinuous, poorly bedded, and very poorly sorted. All the sediments have discontinuous frameworks of boulder to sand-sized grains suspended in a very fine silt-sized matrix.
Clasts are
volcanic quartz, plagioclase, and intraformational lithic material. A variety of different clast types may be seen in one thin section. Most grains are angular but a few are well-rounded.
The sediments were deposited by debris
flows. There is no evidence of traction current activity.
A submarine environment is indicated by brachiopod-bearing siltstones, limestone pods, and deposits of stratiform Cu-Pb-Zn sulphides.
The nature
of vesicles in a lava flow near the base of the formation suggests a maximum depth of deposition of 500m. The lack of tractional reworking indicates a depth below wave base. The sequence was produced by a volcanic pile that grew in moderate depths, with a main volcanic centre along strike to the south.
Clastic material moved
down the flanks by gravity-driven mass flows. The presence of a volcanic pile is supported by facies changes in the overlying Bay and Cunningham Formations.
50
TERTIARY PERMIAN
32DOS-
Grid in metres from 8731 ORANGE and 8732 EUCHAREENA MOO ,000 sheets
Figure 1.
Geology of the Mullion Creek-Kerrs Creek a r e a .
School of Applied Geology, South Australian Institute of Technology3 P.O. Box Ingle Farm> S.A. 5098.
51 THE STRATIGRAPHY OF THE VOLCANIC ROCKS OF THE CUDGEGONG DISTRICT, N.S.W. PEMBERTON, J.W.
Department of Geology, University of Wollongong> P.O. Box 1144,
Wollongong, N.S.W. 2500 In the Cudgegong-Mudgee district a narrow northwest trending tract of Ordovician-Silurian volcanic and sedimentary rocks is flanked by Devonian sedimentary sequences (Fig. 1).
The
oldest rocks are the Cudgegong Volcanics (McManus et al., 1965) comprising a series of massive andesitic lavas and associated immature volcarenites with minor chert lenses.
The Volcanics are
overlain by the Willow Glen Formation (Pemberton, 1980) which consists of chert-bearing conglomerates, fossiliferous limestones, shales and sandstones.
A Silurian age for the unit is
suggested by the brachiopod Kirkidium, halysitid corals, Try-plasma and phaulactid tetracorals and encrinurid trilobites. A series of rhyodacitic lavas with common dacitic, rhyodacitic and chert breccias and minor reworked rhyodacites (Windamere Volcanics - new name) conformably overlies the Willow Glen Formation.
Numerous flow-layered,
conformable rhyolite lenses occur throughout the sequence varying markedly in thickness and outcrop length.
The
Windamere Volcanics are conformably overlain by the Millsville beds (Powis, 1975).
Basal dacitic conglomerates and
rhyodacites bearing chert clasts grade into limestone breccias containing clasts of rhyodacite, rhyolite, sandstone, shale, and chert.
The breccias
grade upwards to limestone with brown shale lenses and rhyodacitic breccia horizons.
The limestones and
shales contain halysitid and heliolitid
52
c o r a l s , together with phaulactid t e t r a c o r a l s , encrinurid t r i l o b i t e s and pentamerid brachiopods, indicating a S i l u r i a n age f o r the M i l l s v i l l e beds.
The beds
are conformably overlain by rhyolite lenses in the western outcrops and are faulted against Early Devonian strata to the southeast. At Cudgegong, the Willow Glen Formation i s probably conformably overlain by the Toolamanang Volcanics (Pemberton, 1980).
However, to the west the con-
tact i s faulted, bringing outcrops of the Toolamanang Volcanics against other menbers of the Ordovician-Silurian sequence.
The Volcanics consist mostly of
massive immature arenites presumably derived from both the Windamere Volcanics and Cudgegong Volcanics. The Ordovician-Silurian strata crop out in a northwest plunging a n t i c l i n e . The Cudgegong Volcanics occur as three narrow wedges in the core of the a n t i cline.
The overlying Willow Glen Formation i s right way up at Cudgegong
whereas to the west the strata are southwest dipping on both limbs, with common small scale a n t i c l i n e s and synclines. limb indicate that i t i s overturned.
Facing c r i t e r i a on the northern
The overlying Windamere Volcanics are
generally massive, yet reworked outcrops to the northwest show ripple marks, channel f i l l structures and c r o s s - b e d d i n g — t h e l a t t e r indicating that the southern limb of the a n t i c l i n e i s right way up.
This i s supported by geopetal
structures in the limestones of the M i l l s v i l l e beds.
The Ordovician-Silurian
rocks are bounded to the northeast by the Cudgegong Fault which separates them from Late Devonian sedimentary sequences, while to the southwest they are faulted against the Early Devonian Queens Pinch Belt (Wright, 1966).
They are
intruded, in the southeast, by the Aarons Pass Granite and in the south are unconforrnably overlain by Permian conglomerate. The Ordovician-Silurian sequence can be correlated, on the basis of l i t h ology and faunal assemblages, with the Sofala sequence of Packham (1969). The tentative correlations are the Cudgegong Volcanics with the Sofala Volcanics; the Willow Glen Formation with the Tanwarra Shale; and the Windamere Volcanics with the B e l l s Creek Volcanics. References McManus, J . B . , McClatchie, L . , and Dickson, T.W., 1965:
Geol. Surv. N.S.W.
Rep34. Packham, G.H., 1968:
Proc. Linn. Soc. N.S.W., 93, 11-163.
Pemberton, J.W., 1980: J. Proc. R. Soc. N.S.W., 113, 49-62. Powis, G.D., 1975:
unpubl. B.Sc. (Hone.) thesis, Univ. of Wollongong.
Wright, A . J . T . , 1966:
unpubl. Ph.D. thesis, Univ. of Sydney.
53
RARE EARTH ELEMENT GEOCHEMISTRY OF CLASTIC ROCKS OF THE TASMAN GEOSYNCLINE
Mukul R . Bhatia Department of Geology and S . R . Taylor Research School of Earth Sciences "The Australian National University Canberra
ACT
2600
Petrological and geochemical studies reveal the diverse nature of source rocks for Tasman Geosyncline (and Hodgkinson Basin) sediments. Rare earth element (REE) chemistry can be correlated with sedimentological variables.
The nature of the source rocks is seen in the systematic variation
in rare earth parameters (EREE, ELREE/EHREE; La/Yb; Eu/Eu*) as the detrital grains change their nature from "juvenile 1 1 volcanic to "mature 1 1 quartzose grains.
Plots of "maturity" indices and REE data demonstrate
the characteristics of each suite of graywackes. Mudrocks are enriched in total rare earth elements (EREE) by about 20% compared with associated graywackes in each suite.
As was the case
for graywackes, the provenance can also be depicted in mudrocks, expressed by clay "maturity" index and REE data. The nature of the sedimentary basin exerts a strong influence on the provenance and the composition of the clastic sedimentary rocks. Rare earth chemistry in conjunction with petrology and geochemistry can be used to distinguish various sedimentary provinces such as magmatic arc, rifted continental margin with orogenic b e l t , collision type and marginal basins of the recycled orogens.
54
MELBOIJENE TROUGH : SEDIMENTATION AND EWIROMENTS
fcy Michael J Garratt Geological Survey of Victoria, Melbourne. ABSTRACT The framework for the analysis of the depositional history of the Melbourne Trough is based on graptolite, conodont, dacryoconaiid horizons, lithofacies characteristics and the changing patterns of brachiopod communities through the Late Silurian-Early Devonian, The abrupt appearance of slumped conglomerates and turbidites at several distinct horizons in the Melbourne Trough sequence is a reflection of discrete bursts of tectonic activity in eastern Victoria and southern New South Wales. Persistent and gradual uplift of the eastern and western margins of the trough through Late Silurian-Early Devonian results in the eastward migration of benttiie communities.
This shallowing results in ^ fringing
of the trough margins by limestone culminating with a thin veneer of non-marine sediments.
55
SOME PROBLEMS IN THE MT READ VOLCANICS, A CAMBRIAN RHYOLITE-DACITE-ANDESITE COMPLEX IN WESTERN TASMANIA Corbett, K.D., Geological Survey of Tasmania, G.P.O. Box 124B, Hobart. The Mt Read Volcanics form a meridional belt about 12 km wide and over 100 km long at the eastern margin of the Dundas Trough.
They abut Precambrian base-
ment on one side and interfinger with, or are faulted against, Cambrian greywacke sequences of fore-arc type on the other.
The volcanics are host to a
number of Cu-Pb-Zn massive sulphide bodies and have considerable exploration potential.
Stable trace element values indicate calc-alkaline affinities.
The contact with the Dundas Trough sediments is generally marked by a sequence of intercalated submarine tuffs, greywackes and shales (western volcanosedimentary sequence) which appears to grade west into typical Dundas Group conglomeratic flysch of Middle to Late Cambrian age.
Sparse fossil and radio-
metric data suggest a similar age for the volcanic sequence.
Various tectonic
models involving a subduction zone in the Dundas Trough have been proposed to account for the volcanics, but a credible subduction complex and the expected deformation and metamorphism appear to be lacking. Flanking the western sequence, and generally having an abrupt or faulted contact with it, is the main central belt of the volcanics, comprising mostly massive rhyolitic to dacitic lavas, ash-flows, breccias, tuffs and intrusives with only minor sediments. very minor basalts.
This belt contains about 15% andesites, but only
The abrupt western contact may reflect a rift or caldera-
type margin in some areas.
Interpretation of the stratigraphy and eruptive
history of these volcanics is hampered by the natural complexity and superposed metamorphic and tectonic effects, and also by the paucity of firm criteria for distinguishing eruptive types and environments and of good facies models applicable to ancient felsic volcanics.
Both marine environments
(indicated by shales, bedded tuffs and massive sulphide bodies) and subaerial environments (indicated by massive pumice-rich welded ash-flows, and breccias with bomb-like clasts) are represented, but actual environments for many rock types remain doubtful.
Other common lithologies include flow-banded, auto-
brecciated and columnar-jointed flows, massive open-framework agglomerates with abundant to sparse rounded clasts up to a metre long, and flows with very elongate wisps apparently transitional between ash-flows and lavas. Models which may have some application to the Mt Read Volcanics are the rhyolitic caldera model, where an intra-caldera complex of lavas, ash-flows, pyroclastics and intrusives is partly ponded within a pre-caldera sequence (e.g. Lipman, 1976); the volcano-tectonic rift model, where an elongate depression filled with thick volcanic sequences occurs within a pre-rift
56
sequence with associated thinner volcanic units (e.g. Burke and McKee, 1979) and the volcanic island model, where a subaerial complex of pyroclastics, flows and domes is flanked by a volcano-sedimentary sequence which may include pyroclastic flows (e.g. Sparks et al., 1980). Burke, D.B. and McKee, E.H., 1979: in central Nevada. Lipman, P.W. 1976:
Mid-Cenozoic volcano-tectonic troughs
Geol.Soc.Amer.Bull., 90, 181-184.
Caldera-collapse breccias in the western San Juan
Mountains, Colorado.
Geol.Soc.Amer.Bull., 87, 1397-1410.
Sparks, R.S.J., Sigurdsson, H. and Carey, S.N., 1980:
The entrance of
pyroclastic flows into the sea, I. Oceanographic and geologic evidence from Dominica, Lesser Antilles.
J.Volcano!.Geotherm.Res., 7, 87-96.
57 MODELS OF CONGLOMERATE DEPOSITION IN BASINS IN THE SOUTHERN TASMAN GEOSYNCLINE. WILLIAMS, P.R. Tasmania
Geological Survey of Tasmania, G.P.O. Box 124B, Hobart,
Flysch sedimentation in the southern part of the Tasman Geosyncline probably commenced in the Late Proterozoic and continued until the transgression of the alluvial fanglomerates of the Owen Conglomerate in the West Coast Range (Late Cambrian - Early Ordovician).
The commencement of
sedimentation was marked by unstable deposits overlying an unconformity in the Pieman River area (Taylor, 1954; E. Williams, 1978; Brown, 1980). Detailed studies of a conglomeratic flysch deposit in south-western Tasmania resulted in the identification of an alternative model for the deposition of conglomeratic flysch than that of a submarine fan/channel model presently adopted in the literature for most flysch deposits.
Strati-
graphic features such as the juxtaposition of various bed thickness variation trends, rapid lithological variations in vertical sequence, and the composition of different bed thickness variation trends lead to the conclusion that straightforward application of the submarine fan model was not acceptable.
Rather, depositional environment adjacent to a developing
fault scarp, fed by numerous shallow channels is envisaged.
In such an
environment abundant debris flow material and other resedimented conglomerate can accumulate over a considerable area, and is not restricted to the spatially minor 1 inner-fan' environment.
The middle fan association is also
different, in that abundant conglomeratic material may accumulate in channelled regions in close juxtaposition to the base-of-slope deposits. These differences are summarised in Table 1.
It is proposed that this
depositional model is applicable to conglomeratic sequences present in the Middle to Late Cambrian Dundas Group, the last flysch-like sedimentary unit of the sedimentary fill of the southern part of the Tasman Geosyncline.
Brown, A.V. 1980. Early deposits in a Lower Palaeozoic Trough of Western Tasmania. 4th Australian Geological Convention Programmes and Abstracts, 1980. Taylor, B.L. 1954. Progress report on the North Pieman mineral area. Unpubl.Rep.Dep.Mines Tasm. 1954; 159-199. Williams, E. 1978. 48; 159-205.
The Tasman Fold Belt system in Tasmania. Tectonophysics
58 TABLE I.
Fades associations Submarine Fans (Walker and Mutti, 1973)
Slope with channels:
Elongate scarp with channels Slope with channels:
F, G, A lf A 3 O elongate bodies, rarely u preserved. cu
F, G, A 1 $ A 2 , A3 shallower channels, wider bodies, not preserved.
a o
Inner Fan:
Base-of-slope:
A]_, A3, G, some F and E. One channel, can migrate.
rare F, A 2 , A 2 , A3, A^, B, C common with interchannel D and E deposits. Reverse grading, outsized clasts, Dominant thinning-upward
•H
sequences.
Number of smaller
channels of variable length and depth (?) V
MT RUGBY FORMATION Middle Fan, channelled:
Channelled deposition region:.
C, D, B 2 , A3, A4 with E. Characterised by thinningupward sequences. Bodies laterally discontinuous.
A 2 , A4 and C dominant, reversegrading still present but rare. Thickening-upward trends occur. Source area control on grain size is implied. Beds discontinuous due to shallow channelling. MT MACKENZIE FORMATION
Middle Fan, depositional lobes: b
2> c> Df E- Characterised by thickening-upward trends. D, C dominant. Insignificant channels, parallel bedding.
Depositional lobes: Channels common, but shallow Facies D, C dominant, but A 2 and A^ common in lobe channels. Characterised by no-trend or symmetrical sequences. NARROWS FORMATION Outer slope deposits: Facies D, E, C. Parallelbedded, typical turbidite structures. No conglomerate deposition. Channels not present. 'Classical1 turbidites. LONG BAY SHALE JOAN POINT SANDSTONE
WALKER, R.G. and MUTTI, E. 1973. Turbidite facies and facies associations, in MIDDLETON, G.V. and BOUMA, A.H. (ed.). Turbidites and deep water sedimentation. 119-157. Soc.econ.paleont.mineral. Pacific Sec : Anaheim.
59
A DYNAMIC FLUVIAL BASIN MODEL FOR THE SYDNEY BASIN by P.J. Conaghan, J.G. Jones, K.L. McDonnell & K. Royce School of Earth Sciences, Macquarie University, North Ryde. ABSTRACT
Along the northeastern margin of the Sydney Basin the basinal succession is sharply transected by the northeasterly-dipping frontal thrust faults of the Tamworth Arc of the New England foldbelt, to which the Sydney Basin constituted a foredeep in the Late Permian and Triassic.
Southwestwards it
turns to a ragged erosional edge on the foreland basement constituted by rocks of the early/mid Palaeozoic Lachlan Fold Belt.
In its present gross
form the Basinal sediment wedge is gently warped about a median NW-SE axis which intersects the coast at Sydney. The northern limb of the Basin along the coast between Sydney and Newcastle exposes 1200m of the upper part of the 1500m Late Permian and Triassic succession.
Of this part of the succession exposed along the coastal transect
the lower 800m (hereafter the "labile facies") consists of conglomerate, sandstone, mudstone, tuff and coal.
Rock fragments plus feldspar constitute
50% or more of the clastic component of the sandstone.
The mean crossbed dip
azimuth (CDA) within this interval is westsouthwest (249°).
The uppermost 80m
of the succession (hereafter the "quartzose facies") comprises quartz sandstone (quartz>> 95%) with subordinate mudstone; CDA in this facies is towards the northeast (mean 049°).
The intervening strata (the "mixed facies") are
sandstones and mudstones intermediate in composition (quartz = 50 - 95%), and in CDA, which is southsouthwest anticlockwise through to northeast (mean 112°). Thus the succession is characterized by two salient up-sequence trends: a radical change in composition, expressed most clearly in the increase in quartz/ labile ratio, and a progressive anticlockwise swing in CDA from southwest through southeast to northeast.
Environmental analysis indicates that the
exposed succession is of fluvial and fluvio-lacustrine affinity. The features of the north coast succession are most simply explained in terms of a fluvial drainage network in which the labile facies is deposited by southwesterly-flowing tributaries, the quartzose facies by northeasterlyflowing tributaries, and the mixed facies by a southeasterly-flowing axial trunk stream.
The progressive up-sequence change in sediment composition and
CDA is taken to express progressive displacement of the drainage net towards the northeast. supply.
This migration is related to a changing balance in sediment
The successions exposed on the south coast between Wollongong and Sydney, and in the Blue Mountains between Kanangra Walls and Kurrajong, show the same gross up-sequence trends in sediment composition and CDA, confirming the basin-wide applicability of the model. Inherent in the model is the diachroneity of the boundaries delineated between strata of quartoze, mixed and labile facies.
In terms of the
postulated northeasterly migration of facies domains in time, these boundaries should become younger towards the northeast.
The microfloral zone boundaries
recognized by Helby (1973) are, with one exception, facies discordant.
The
lowermost one marks the transition from the Permian Striatetes Microflora to the almost wholly Triassic Falcisporites Microflora.
Followed to the southwest
it is seen to move from within the labile facies on the north coast to the boundary between labile and mixed facies in the Blue Mountains.
The succeeding
two microfloral zone boundaries are similarly conspicuously facies discordant. The uppermost one, followed from northeast to southwest, moves from the upper boundary of the labile facies to the lower boundary of the quartzose facies. If these zone boundaries are time-parallel, as seems plausible, the expectations of the model are amply confirmed: the facies boundaries are time transgressive and they young towards the northeast.
Reference:
HELBY, R., 1973 : Review of Late Permian and Triassic palynology of New South Wales. Spec. Pubis Geol. Soc. Aust., 4, pp. 141-155.
61
Late Palaeozoic mass-flow deposits of a lower trench-slope setting, northeastern New South Wales C.L. Fergusson, Department of Geology, University of New England, Armidale Abstract The Coffs Harbour Beds are exposed in the southern portion of the faultbounded Coffs Harbour Block, in the eastern part of the New England Fold Belt. They are a thick (tens of km) volcaniclastic flysch which is conformably overlain by a thick sequence of argillites. Five sedimentary facies are recognized in the Coffs Harbour Beds on the basis of distinctive bed form, bed thickness, grain size and sedimentary structures.
These include:
thinly bedded flysch, argillites, thickly
bedded sandstones, minor flyschoid sandstones and resedimented conglomerates. Most beds within these facies can be described internally by the Bouma sequence Beds of the thickly bedded sandstone facies can be described internally by an extended Bouma sequence nomenclature proposed by Cas (1979).
These facies
are broadly equated with submarine fan facies of the Mutti-Ricci Lucchi classification.
Two facies associations are identified:
a basin plain
association of thinly bedded flysch, argillites and minor thickly bedded sandstones;
and, an outer fan association of thinly bedded flysch, thickly
bedded sandstones, minor argillites, flyschoid sandstone and resedimented conglomerates. The structural style of the Coffs Harbour Beds is similar to that developed in accretionary prisms adjacent to oceanic subduction zones (Fergusson, in prep.).
The basin plain and outer fan sedimentary environments
of these rocks are consistent with their being a trench slope basin or apron deposit formed on the lower trench-slope of a Late Palaeozoic subduction zone complex within the New England Fold Belt.
CAS, R., 1979:
Mass-flow arenites from a Palaeozoic interarc basin, New
South Wales, Australia:
mode and environment of emplacement. Jour.
Sed. Petrology3 49, 29-44. FERGUSSON, C.L., in prep.:
Pre-cleavage regional folds in the Late Palaeozoic
Coffs Harbour Beds, northeastern New South Wales.
J. geol. Soc. Aust.
62 PETROFACIES AND PETROLOGIC EVOLUTION OF SANDSTONES IN THE COFFS HARBOUR BLOCK, NEW ENGLAND OREGON
R.J. KORSCH
Armidale College of Advanced Education, Armidale, N.S.W.
2350
The Coffs Harbour Block, in the eastern part of the New England Orogen, consists of a very thick, monotonous sequence of Late Palaeozoic turbiditycurrent derived greywacke, laminated siltstone and mudstone, and massive argillite.
The sequence coarsens upwards, and is subdivided into three
stratigraphic units (Moombil, Brooklana and Coramba Beds).
Although
sandstones display both vertical and horizontal detrital compositional variations, the sequence as a whole is marked by having a common provenance. It was derived predominantly from a volcanic arc source consisting of mainly dacite with minor andesite and rhyolite. common than pyroclastics.
Flow detritus is more
Rare, but persistent, components are basic
volcanics, acid plutonics, low-grade metamorphics and radiolarian chert. The Coramba Beds are divided into four petrofacies, based on QFR data and the occurrence of detrital hornblende: PETROFACIES IN THE CORAMBA BEDS
Petrofacies D Petrofacies C Petrofacies B Petrofacies A
QUARTZ
HORNBLENDE
L:F
QFR
low low low low
present present absent absent
L>F F>L F>L L>F
Ql 8 Fi7«B5 QIS Fs^Rai Q 18 F58:R21+ Ql2 Fi 8 R7 0
The Moombil Beds have sandstone compositions similar to Petrofacies A, and in the Brooklana Beds sandstones similar to both petrofacies A and B occur. Vertical variation in minor components, including detrital biotite, chlorite and plutonic, metamorphic and metasedimentary fragments indicate an increase, in the number of sandstones containing these components, upwards from the Moombil Beds to Petrofacies A, suggesting erosion and exposure of a non-volcanic source.
A sudden decrease occurs in Petrofacies
B, along with an increase in the abundance of feldspar suggesting recommencement of volcanism penecontemporaneous with sedimentation.
From Petrofacies
63
B through Petrofacies D another increase in minor detrital components occurs, indicating further erosion of the non-volcanic source area.
The
lack of significant variation in detrital components, with the predominance of dacitic detritus throughout the sequence, indicates little temporal change in the character of the volcanic detritus shed from the magmatic arc.
The influx of feldspar in Petrofacies B is interpreted as due to
recommencement of volcanism with penecontemporaneous reworking of tuffaceous horizons and deposition, rather than a change in the nature of volcanism in the arc. Korsch
(1977) recognised several lithological associations in the
New England Orogen east of the Peel Fault.
The Coffs Harbour Association
includes the Coffs Harbour Block and, as well, occurs in several separated structural blocks east and south of Armidale.
In these blocks, equivalents
of the Coramba petrofacies are recognised, although because of structural complexity, a complete A-D sequence has not been found.
With one exception,
other associations have similar QFR plots to the Coffs Harbour Association suggesting a common provenance for much of the New England Orogen. The Coffs Harbour sandstones are similar to sands occurring in modern ocean basins which have been derived from an arc system of either continental margin or island arc type (Dickinson & Valloni, 1980).
Also, the
sequence correlates with the undissected to transitional magmatic arc provenance of Dickinson & Suczek (1979) and the predominance of volcanic over all other lithic detritus indicates that unroofing of the plutonic rocks in the arc has not occurred to any marked extent.
The sandstones
are not similar to the recycled orogen provenances such as accretionary prisms or trench-slope basins (Dickinson & Suczek, 1979; Moore, 1979; Korsch, in prep.). DICKINSON, W.R. & SUCZEK, C.A. 1979 Plate tectonics and sandstone compositions. Am. Assoc. Petrol. Geol. Bull., V.63, pp.2164-2182. DICKINSON, W.R. & VALLONI, R. 1980 Plate settings and provenance of sands in modern ocean basins. Geology3 V.8, pp.82-86. KORSCH, R.J., 1977 A Framework for the Palaeozoic geology of the southern part of the New England Geosynchne J.geol. Soo. Aust., V.25, pp.339-355. MOORE, G.F., 1979 Petrography of subduction zone sandstones from Nias Island, Indonesia. J. Sedim. PetrolV.49, pp.71-84.
64
PALAEOGEOGRAPHIC SIGNIFICANCE OF LATE CARBONIFEROUS PYROCLASTICS, WERRIE SYNCLINE, N.S.W.
J. Fergusson, Department of Geology, University of New England, Armidale. Abstract The Late Carboniferous volcaniclastic Currabubula Formation exposed in the Werrie Syncline (Carey, 1934) and adjacent fault blocks along the western margin of the Tamworth Belt, consists of silicic pyroclastics interbedded with fluvial and fluvioglacial conglomerates, sandstones and minor mudstones.
Four
dacitic to rhyodacitic crystal-rich pyroclastic units outcrop throughout much of the Werrie Syncline, and in the nearby Quirindi Dome and Carroll-Clifton Block.
The oldest, an ashfall tuff, has been traced along strike for 55
kilometres and covers an area of at least 1000 square kilometres.
The three
younger pyroclastics are all ashflow tuffs, mappable along strike for up to 30 kilometres. East-west thickness variations and/or internal facies changes within these pyroclastic units confirm an eruptive source to the west.
Detailed mapping of
the units also allows recognition of major eastward-trending distributary channels within the Currabubula Formation. The pyroclastic stratigraphy established for the Werrie Syncline cannot be correlated with that exposed in the extreme south of this fold, nor with that in the Castle Mountain Dome, or at Kankool.
Similarly, the numerous coeval
pyroclastics in the Rocky Creek area, 120 kilometres to the north, defy close correlation with those of the Werrie Syncline.
Thus in Late Carboniferous
times, three separate eruptive centres were active, each delivering distinctive pyroclastic debris to the Rocky Creek, Werris Creek, and upper Hunter districts. Reference CAREY, S.W., 1934:
The Geological Structure of the Werrie Basin.
Soc. N.S.W.3 59, 351-374.
Proo. Linn.
65
EARLY CARBONIFEROUS SEDIMENTATION IN THE SOUTHERN NEW ENGLAND BELT I.D.Lindley, School of Applied Geology, University of N.S.W.
EARLY Carboniferous volcaniclastic sedimentation in the southern New England Belt is related to a large resurgent volcano-tectonic depression the shape of which was controlled by regional faults.
Both marine and non-marine sequences in
the belt reflect the 6 stages of the resurgent caldera cycle proposed by Smith and Bailey (1968). During the Tournaisian (Schel1wiene11a cf• burlingtonensis Zone) stable marine conditions existed throughout most of eastern Australia.
The onset
of instability in the southern New England Belt is indicated by late Tournaisian (Pustula gracilis Subzone) pyroxene andesitic and dacitic volcanism restricted to the margins of the region.
Concurrent regional
doming (Stage I) related to the near-surface emplacement of magma culminated with rapid marine regression and unconformity during the middle Visean.
Regional doming was terminated during the late Visean by eruption of large volumes of ignimbrite (Stage II).
Progressive collapse, concurrent with
eruption, resulted in the transgression of marine sediments of the Orthotetes australis
Zone.
As a consequence of the eruptive removal of magma, major
collapse followed (Stage III).
A brief period of preresurgence sedimentation (Stage IV) immediately followed collapse, with the deposition of turbidite sequences in excess of 1000m thickness.
Onset of resurgent doming (Stage V) resulted in the rapid
shallowing of the turbidite basin.
Breaching of the doming surface during
the late Visean (Delepinea aspinosa Zone) marked the commencement of Stage VI volcanism, resulting in at least 5 separate eruptions of rhyolitic lavas interbedded with non-marine sediments.
Termination of the Early Carboniferous resurgent cycle is indicated by a return to andesitic volcanism during the latest Visean. References: Smith, R.L., and Bailey, R.A., 1968.
Resurgent cauldrons, in Coats, R.R.,
and others, eds., Studies in volcanology: p.613-662.
Geol. Soc. America. Mem0 116:
66
POSTER SESSION
1 - 2 December
67
TECTONIC CONTROLS ON THE DISTRIBUTION OF LAMB IAN FACIES BASINS IN NSW AND VICTORIA Keith A.W. Crook Department of Geology, ANU, Canberra
2600
Sediments of the flLambian facies,? form a major part of most Middle Paleozoic transitional realm tectonic units in southeastern Australia (Fig. 1).
Typically they are fluvial or paralic red-bed sequences
composed predominantly of sandstone and mudstone with subordinate amounts of conglomerate.
Rarely, in the vicinity of oblique-slip faults, grey to
black lacustrine sediments occur.
These may include a flysch lithofacies
(Fergusson et al. 1979, Crook & Scott 1980).
Silicic or in some cases
bimodal silicic-mafic volcanics occur in some sequences, most commonly in their lower parts (1, 2, 8, Fig. 1) (Marsden 1976, Fergusson et al.1979). Rarely volcanics predominate and are associated with cauldron structures (7: Fig. 1) (Marsden 1976). Most of the transitional realm sequences in southeastern Australia occur in relatively small elongate basins, many of which are synclinal (Fig. 1).
Several of these basins are bounded by faults on at least one
side; in some at least, faulting has controlled the pattern of sedimentation (Fergusson et al. 1979).
These elongate basins are intramontane depressions,
inter-deeps and volcanic rift zones (Scheibner 1976). The transitional realm sequences of the Upper Devonian Ravendale Basin (14, Fig. 1) is more extensive.
It constitutes a terrestrial or continental
basin (Scheibner 1976). The distribution of many of these basins is closely related to earlier patterns of volcanic arc and fore-arc development, as follows.
Transitional
realm basins develop above subsided volcanic arcs in many arc terrains (Crook, 1980) (1-5, Fig. 1), and above the outer and inferrentially thinner parts of accretionary prisms (7, 8, 10, Fig. 1), even where these are buried beneath post-arc flysch.
Indeed many of the transitional
realm basins are associated with arc terrains which include thin accretionary prisms. Other transitional basins are evidently related to the narrower Siluro-Devonian extensional features (11-13, Fig. 1), whose sedimentary fill they either overlie or adjoin.
In general they are not associated
with the larger, flysch-filled extensional features.
The tectonic
antecedents of the Ravendale Basin (14, Fig. 1) are uncertain: the basement
68
is not exposed, outcrop is indifferent, and the area is little studied. Apparently, transitional realm basins, and the earlier extensional features with which some are associated, form in response to local deficiencies in crustal thickness and strength which are manifested as kratonization proceeds, particularly during the penultimate phase of kratonization immediately preceding the attainment of kratonic stability These deficiencies are ultimately attributable
to the development
patterns of the volcanic arcs and accretionary prisms which form the basement and provide a framework for younger deposits. CROOK, K.A.W., 1980.
J. struct. Geolin
CROOK, K.A.W. & SCOTT, P.A., 1980. FERGUSSON, C.L., et al.3 1979. MARSDEN, M.A.H., 1976. SCHEIBNER, E., 1976.
press.
Submitted to J. sedim. Petrol.
J. geol. Soc. Aust26,
87-105.
Spec. Publ. geol. Soc. Aust., 53 77-124.
Explanatory notes on the tectonic map of New
South Wales. Geol. Surv. NSW, Sydney, 283p.
32°-
[••';•;.'] cover rocks ^J extensional features |
sediments
I J. E
36°-
volcanics
rocks of the transitional tectonic realm
arc terrains mafic, predom. silicic arc volcanics
Dm-Du
f ~ J ] PG kraton V boundaries of j arc terrains
i
144°
Fig. 1:
148°
200km i
/T\ vV
localities (see text)
I
152°
Distribution of Lambian, and Permo-Triassic (6,9) transitional realm basins.
69
FORE-ARC EVOLUTION AND CONTINENTAL GROWTH:
A GENERAL MODEL
Keith A.W. Crook Geology Dept., Australian National University Canberra, 2600 Australia ABSTRACT The extended evolution of fore-arc regions which leads to their eventual incorporation into stable kratonic continental crust is elucidated by a general model based upon observations from the modern circum-Pacific and the Paleozoic Tasman Geosyncline. Fore-arc regions widen during subduction in the manner described by Karig & Sharman (1975; Geol. Soc. Am. Bull.).
Their history after subduction
has ceased depends upon the thickness of the accretionary prism formed during subduction.
Where the prism is thick (ca. 20 km) kratonization is a
single-step process.
The fore-arc region remains above sea-level; post-arc
silicic volcanics accumulate due to granitoid plutonism, the magmas being derived by melting of the subduction complex and from the oceanic lithosphere trapped beneath it.
The volcanic arc sinks, becoming the site of a fore-deep.
Intermediate-thickness accretionary prisms (ca. 16 km) are kratonized in a two-step process.
They remain at shelf depths, while their associated
volcanic arcs sink to comparable depths.
Both acquire a post-arc shallow
marine sequence of typical platform-cover facies.
They are then deformed and
intruded by granitoids when the crust attains critical thickness (ca. 20 km). Thin accretionary prisms (£12 km) require a three-step process for kratonization.
They and their associated arcs sink to bathyal depths.
They
are overwhelmed by prograding post-arc flysch deposits of continental origin. Deformation of the post-arc flysch and plutonism occur when critical crustal thickness (ca. 20 km) is attained.
A transitional tectonic regime ensues, with
molasse-like transitional basins preferentially sited over the extinct volcanic arcs and the thinner parts of buried accretionary prisms. The model satisfactorily explains the Late Proterozoic-Paleozoic evolution of southeast Australia, where a 1000km wide tract of continental crust was accreted to the Australian Kraton in 250-300 m.y., beginning as a SW Pacific-type oceanic terrain.
It has been found useful for interpreting
geosynclinal terrains in other continents. According to the model, the dynamic processes that contribute to kratonization are systematically causally connected.
Kratonization is a
70
unified, internally deterministic and self-sustaining phenomenon. model has implications for the origin,
'stratigraphy*
of upper and lower continental crust; the origins and tectonic of ophiolites, granitoids, paired metamorphic belts and basins; and for the nature and causes of
volcanic arc
The
and composition settings
transitional
orogenesis.
subduction complex
fore - arc sequence
trench oceanic crust
y accretionary
prism
ophiolite Benioff
Zone
volcanic arc
f o r e - a r c sequence disrupted
subduction complex uplifted
THICK sed. basin on old volcanic arc
THICKNESS OF ACCRETIONARY
post-arc >'volcanics
mmmwmm 'underthrust slab modified to form lower continental crust
accretionary prism
INTERMEDIATE
volcanic arc extinct
PRISM
shallow marine post-arc sequence of platform cover facies-
underthrust slab stationary, not yet modified
deformation of post-arc sequence and plutonism
KRATON (underthrust slab modified to form lower continental crust
KRATON
volcanic arc buried by flysch
sea level-^ prograding post-arc flysch ^^eclge
f * i un derthrust slab stationary, not yet modified deformation of post-arc flysch and plutonisjTjj^
mMWMmmmm funderthrust slab modified to form lower continental crust
(40
TRANSITIONAL TECTONISM KRATON
71 THE EARLY DEVONIAN TANGERANG VOLCANICS, N.S.W.
CARR, P.F. & JONES, B.G.
Department of Geology, University of Wollongong,
P.O. Box 1144y Wollongong, N.S.W. 2500 The Tangerang volcanics occur in the Marulan South
—
Bungonia region, N.S.W.
(Fig.
1), and
have previously been described from the southern part of this area by Carr et al. (in press). sequence is composed of interbedded sedimentary
rocks
conformably
overlie
and
lensoidal
the
Late
Devonian Bungonia Limestone.
The
volcanogenic
dacites
Silurian
which
to basal
The western bound-
ary of the formation is an intrusive contact with the
Marulan
Batholith.
Preserved
thicknesses
range from 450m to 1600m. Open, gently plunging folds occur in the Marulan South region, but the sequence has consistent westerly dips between 35° and 55° near Bungonia. and
associated
The Windellama Limestone
volcanogenic
sedimentary
rocks
which occur 15 km south of Bungonia are probable lateral
equivalents of the Tangerang
volcanics.
An Early Devonian age of the latter sequence is indicated
by
its
stratigraphic
included faunas at Windellama
position,
the
(Mawson, 1975) and
radiometric dating of the Marulan Batholith (Carr
et aUt 1^80) The dacites contain phenocrysts of plagiocl ase (An
) and embayed quartz set in a very
fine-grained
groundmass
K-feldspar sthene
and
graphically phenocrysts.
Fig. 1 Simplified geological map of the Marulan South—Bungonia region, N.S.W.
of quartz, plagioclase,
and minor hornblende, biotite, hyperiron-titanium youngest
oxides.
The
dacites contain
strati-
hornblende
Interbedded sedimentary rocks range
from
very coarse-grained, poorly
and
litharenites
sorted
arkoses
to
well
sorted,
fine-grained
quartz-rich
arenites
and
minor
(Fig. 2).
Most arenites contain angular grains
cherty
shales
of plagioclase, 3-quartz and volcanic rock fragments in a chloritic and cherty matrix.
72
QUARTZ
097 (24) FELDSPAR
Fig. 2 Mineralogical composition and classification of arenites in the Tangerang volcanics.
Fig. 3 Palaeocurrent directions in the Tangerang volcanics.
The Tangerang volcanics represent an accumulation of shallow-marine arenites interbedded with submarine dacitic lavas and associated pyroclastic rocks. Sporadic occurrences of crinoid ossicles, bryozoans and solitary corals occur in the lower and middle parts of the formation.
Bedding in the coarse arenites
ranges from poor to massive whereas the fine arenites are irregularly and finely wavy-laminated, flat-bedded, cross-bedded or massive.
The cross-bedding ranges
from small-scale sinuous current ripples to medium-scale tabular cross-beds.
In
addition, scour and fill structures, small slump folds and thin lenses of finegrained conglomerate are present in the arenites.
The strongly bimodal palaeo-
current pattern (Fig. 3) probably represents a combination of offshore (eastward) and longshore (northward) migration of subaqueous dunes along the eastern margin of the Capertee Volcanic Arch.
The main volcanic activity was centred to
the northwest of Marulan South and also was responsible for the emplacement of the correlative Bindook Porphyry. detritus was contributed
At the same time, fine-grained quartzose
to the depositional area, possibly from an exposed
block of the Ordovician Tallong Beds.
References Carr, P.F., Jones, B.G., Kantsler, A.J., Moore, P.S. and Cook, A.C., (in press): The Geology of the Bungonia District, New South Wales.
Proc. Linn. Soc.
N.S.W. Carr, P.F., Jones, B.G. and Wright, A.J., 1980: Bungonia District, New South Wales. Mawson, R., 1975:
Dating of Rocks from the
Proc. Linn. Soc. N.S.W.j 104, 111-117.
The geology of the Windellama area, New South Wales.
R. SOC. N.S.W.j 108, 29-36.
J. Proc.
73
H0L0C3NE SEDIMENTS AND MOLLUSCS IN SYDNEY HARBOUR J . E . Carey School of Earth Sciences, Macquarie University Dredging and drilling in Sydney Harbour tributaries show that in muddy sands at -8m to -10m there is an abundant and diverse estuarine mollusc fauna dated 5000-6600 years B.P., dominated by large thick-shelled filter-feeding bivalves including Ostrea angasi, Proxichione materna and Anadara trapezia, with the scallop Notovola fumatus.
The overlying sediments are peats and sandy muds
with abundant charcoal; the underlying sediments to -18m (circa 11000 B.P.) are fluvial muddy sands and valley floor clays with minor charcoal. shell-rich layers are present in other east coast estuaries*
Similar
Many species
of the older fauna are now extinct or greatly depleted in the Sydney Harbour locations.
The present fauna comprises mainly gastropods including
Velacumantus australis and Prothalotia contessi together with small thin-shelled bivalves.
The old bivalves are bored by algae and clionid
sponges and were infested during life with commensal ?spionid polychaetes. This mudworm infestation would not have been lethal, but combined with the effects of the changing sedimentary regime as sea level rise ended, and possibly with over-fishing by aborigines, it may have contributed to the rapid decline of the larger shellfish.
74
SEDIMENTOLOGY OF SPENCER GULF R.V. Burne Baas Becking Geobiological
Laboratory
Canberra
Spencer Gulf is a funnel shaped extension of the
Southern
Ocean into the southern semi-arid margin of the Australian continent.
It is an area of temperate carbonate
sedimentation
dominated by molluscan, foraminiferal, and algal remains
which,
in the shallow northeastern portion of the Gulf, is characterised by a variety of sub-tidal, sea-grass environments.
The
powerful tidal regime and wind-generated wave action give rise to the shoreward
transport of a proportion of the
carbonate
sediment, and this, possibly coupled with Holocene uplift, has resulted
in the progradation of shorelines and the formation of
a number of regressive paralic sedimentary
complexes,
along the northeastern
Precise levels
shore of the gulf.
especially along
transects were matched with tidal inundation data in order to reach an understanding areas.
of the environmental zonation of these
Two types of shoreline characterise
complexes:
exposed
the prograding
shorelines have beach ridges lying high on
a broad intertidal plain:
protected
shorelines are the sites
of mangrove colonisation, where trees rising close to low water trap fine-grained
sediment.
This type of coast is cut by
tidal
creeks which serve to drain intertidal marshes in the lee of the mangroves.
Cyanobacterial mats colonise parts of the high
intertidal and supratidal zones of the prograding
complexes.
Three mat types are recognised, and are referred
to as smooth,
crenulate, and tufted. evolved
The coastal carbonate complexes have
in a post-depositiona1 hydrological regime determined
continental groundwater movements of the semi-arid
zone.
by
There
is sufficient rainfall in the vicinity of Spencer Gulf to ensure the discharge of saline continental groundwaters as springs in the coastal zone. and produce significant
supratidal
These spring waters then
precipitation of aragonite, halite, and iron minerals. is, however, insufficiently marine
evaporites.
evaporate
accumulations of gypsum, as well as local
arid for the formation of
The area extensive
75
THE
KOWMUNG
ORIGIN,
VOLCANICLASTICS:
NORTHEASTERN
LACHLAN
A
DEEP-WATER
FOLD
BELT,
SUCCESSION
OF
MASS-FLOW
N.S.W.
R.A. CAS,1 C.L. FERGUSSON,2>3 J. FERGUSS0N,2>3 J.G. JONES,2 C. McA. POWELL2 and W.D. ROOTS2.
department of Earth Sciences, Monash University, Clayton, Victoria, 3168. 2
School of Earth Sciences, Macquarie University, North Ryde, N.S.W., 2113.
^Department of Geology, University of New England, Armidale, N.S.W., 2351.
The Lower to ?Middle Devonian Kowmung Volcaniclastics form the upper part of a succession of Upper Silurian to mid-Devonian flyschoid rocks in the Yerranderie area of New South Wales.
Two macrofacies occur:
1. a muddy
macrofacies, which represents the ambient, background sedimentation and consists of graded-bedded to massive siltstones, sandstones, conglomerate, bedded limestone and large allochthonous limestone blocks interbedded within pervasive mudstones.
Bouma sequences are common, sole structures also occur
and bedding is up to 3 metres thick;
2. a volcaniclastic macrofacies, which
intrudes and interrupts the accumulation of the ambient muddy macrofacies, and contains massive to partly graded quartzo-feldspathic siltstone, sandstone, gritstone, breccia and conglomerate.
Sedimentation units are up to 120 metres
thick.
The relationship between the two macrofacies is an interdigitational
one.
During breaks in the influx of volcaniclastic sedimentation units, the
ambient muddy macrofacies recurred. both macrofacies was mass-flow:
The dominant transportational process in
granular mass-flows (turbidity currents,
grain-flows), debris flows and avalanches.
Massive, mudstones are hemi-
pelagic in origin.
The provenance is diverse.
In the muddy macrofacies framework grains in the
finer sediments are microlitic volcanic rock fragments, minor volcanic quartz and plagioclase, suggesting a mafic to intermediate volcanic source.
In the
conglomerates and breccia, clasts include indurated quartzite and vein quartz, both consistent with derivation from regionally extensive, deformed Ordovician quartz-rich flyschoid successions. also occur.
?Penecontemporaneous limestone clasts
In the volcaniclastic macrofacies, angular volcanic quartz, and
feldspars variously associated with altered angular vitriclasts make up the sandstones.
The breccia consists of angular brown, green and pale yellow
dacite fragments.
In the conglomerate,clasts of quartzite, limestone, dacite
lava and lenticle tuff predominate. vary laterally.
However the proportions of these clasts
The volcaniclastic macrofacies
sediments were probably
derived from the nearby, coeval Bindook Complex which consists of silicic ash-
76 flow and ash-fall tuffs, lavas, associated sediments and granitoids.
Both macrofacies were deposited in relatively deep-water.
The volcaniclastic
macrofacies probably represents a submarine volcanic apron around an emergent volcanic complex.
Clasts were worked in fringing littoral and fluvial
environments or were derived directly from volcanic eruptions. quartzites were probably also exposed as headlands.
Ordovician
Although the succession
grossly coarsens upwards, it is doubtful whether a submarine fan environment fed by a single point source is applicable. point sources were operating.
There is evidence that several
The extremely thick volcaniclastic sedimentation
units would in any case have subsumed and overflowed pre-existing depositional topography. Stratigraphically the base of the Kowmung Volcaniclastics is taken at the first sedimentation unit of the volcanic macrofacies.
The muddy macrofacies below
this level is part of the Siluro-Devonian Taralga Group.
77
FIELD GUIDE EXCURSION 1
78
EXCURSION ONE:-
SILURO-DEVONIAN VOLCANOGENIC SEDIMENTATION IN THE LACHLAN FOLD BELT
by M. OWEN (BMR) and R. CAS (MONASH UNIV.)
INTRODUCTION Detailed research on the widespread Palaeozoic felsic volcanic rocks of the Lachlan Fold Belt has for long been a sadly neglected field of study with the result that they probably constitute the most poorly known group of rocks in the Fold Belt.
A multitude of undefined and often
undescribed units have been named, many of which only appear in the legend of a geological map, and little is known about the relative age of most of these units or their stratigraphic relationships.
This is a surprising
situation given their status as one of the most economically prospective groups of rocks within the Fold Belt for base metal mineralization. In recent years this situation has begun to be remedied and this excursion will attempt to show some of the advances that have been made in both stratigraphic and environmental aspects of volcanic sequences in two contrasting areas, the dominantly subaerial Canberra-Yass Shelf and the submarine Hill End Trough. M. Owen has written the text for the first and second days and R. Cass has written the text for the third day.
79
DAY 1
3rd December, 1980
VOLCANIC ROCKS OF THE CANBERRA REGION
INTRODUCTION The Palaeozoic volcanic stratigraphic of the Canberra area has, in recent years, undergone a major revision, the magnitude of which is perhaps best illustrated by the Narrabundah Ashstone, which was considered by Opik (1958) as the final volcanic event in the Palaeozoic of the Canberra area, of Early Devonian age, but which is now considered to be the earliest, of Middle Silurian age.
The earlier stratigraphy, as described by Opik,
and the present one, as revised by officers of BMR, are compared in table 1. Concurrently with the greater understanding of the stratigraphy of the Canberra area, there has been a steady increase in appreciation of the mode of emplacement of many of the volcanic rocks, and while
much remains
tp be done, the broad outlines are apparent,
SUMMARY OF VOLCANIC STRATIGRAPHY The volcanic rocks of the Canberra area can, on chemical and petrographic grounds, be divided into two suites, here termed the Hawkins Suite and the Laidlaw Suite, with the Hawkins Suite being the older stratigraphically.
Both Suites contain several formations.
The Hawkins Suite in the Canberra area can be divided into four formations, the Ainslie Volcanics, Paddys River Volcanics, Walker Volcanics and Mt Painter Volcanics,
All are characterised by a phenocryst
mineralogy of quartz + plagioclase (usually altered to albite) + biotite + cordierite
hypersthene
to S-type granites.
accessory garnet, and by close chemical similarities
Alteration of all mafic minerals except garnet to
chlorite is ubiquitous, however detailed petrographic work has enabled the consistent recognition of these altered phenocrysts, The Ainslie and Paddys River Volcanics are probably correlatives, and are the oldest volcanic units in their respective areas (Canberra and Cotter Dam).
Both consist of a varied sequence of dacitic to andesitic
ignimbrite, airfall tuff and agglomerate, however the Paddys River Volcanics
OPIK 1958 CANBERRA LOWER DEVONIAN
PRESENT CANBERRA
WORK
COTTER
YASS
NARRAB. ASHSTONE AINSLIE VQLCANICS
BARAMBOGIE GROUP
UPPER SILURIAN
MUGGA PORPHYRY (intrusive)
PAINTER PORPH. (intnueive)
BOOROO PONDS GROUP eroded LAIDLAW
YARRALUMLA FM.
80
PEAKIN VOLCANICS
FAIRBURN GR.
DEAKIN VOLC.
CANBERRA FM.
CANBERRA GR.
VOLCANICS SWAMP CR. VOLCANICS
YARRALUMLA FM." MT. PAINTER VOLCANICS AINSLIE VOLC.
MIDDLE SILURIAN
SILVERDALE FORMATION
top
YASS FORMATION WALKER VOLC. PADDYS RIVER VOLCANICS
INARRABUNDAH
HAWKINS VOLCANICS
ASHSTONE|
LOWER SILURIAN Table
1: Comparison of Opik 1958 with present BMR interpretation for Canberra and correlation with Cotter and Yaee.
81
also contain some marine limestone and shale.
Notwithstanding these
marine rocks, much of the Paddys River, and all of the Ainslie Volcanics are considered subaerial.
The Ainslie Volcanics rest conformably on the
shallow marine Canberra Formation (which itself contains detrital felsic volcanic material) and the Paddys River Volcanics rest unconformably on Ordovician flysch. The Paddys River Volcanics are overlain in the Cotter Dam area by the Walker Volcanics, a sequence of dacitic ignimbrite and air fall tuff, the most characteristic feature of which is its reddish purple colour. Hypersthene phenocrysts and garnet xenocrysts are also markedly more abundant than in the older unit.
Several sedimentary lenses are present
within the Walker Volcanics, with that at Coppins Crossing, just west of Canberra, being richly fossiliferous. The Mt Painter Volcanics were considered to form an intrusive sill by Opik (1958), however it is now recognized that it displays many of the classic characteristics of ignimbrites,
A feature of the unit is
the abundance of lithic fragments of country rock, and also garnet xenocrysts. It appears to be essentially one ignimbrite cooling unit, possibly up to 200 m thick, and can be traced over a strike length of probably 40 km. The relationship between the Mt Painter Volcanics and other members of the Hawkins Suite in the Canberra area is obscured by faulting, however it appears certain that it must be the youngest member of the Suite. The Mt Painter Volcanics are overlain conformably by a dominantly clastic, shallow marine unit, the Yarralumla Formation, which shows rapid variations in thickness, and which is considered to correlate with the Yass Formation from the Yass area, though the two are not in outcrop continuity. The Laidlaw Suite, which overlies the Yarralumla Formation apparently conformably in Canberra, can be divided into three units, the Deakin Volcanics, Laidlaw Volcanics and Swamp Creek Volcanics.
Overall
mineralogy is similar for the three units, and consists of quartz + plagioclase (often un-albitised and strongly zoned with cores of labradorite) + sanidine + biotite + hypersthene.
Garnet and cordierite are never found,
while allanite (unknown in the Hawkins Suite) is a common accessory in the
82
Laidlaw and rare accessory in the Swamp Creek Volcanics.
Chemically the
Laidlaw Suite has more in common with I-type rather than S-type granites. The Deakin Volcanics are the oldest of the Laidlaw Suite in Canberra, resting conformably on the Yarralumla Formation.
The unit
consists of a varied sequence of ignimbrite, lava, airfall tuff and local fluviatile sediments, with some horizons showing a reddish-purple alteration reminiscent of the Walker Volcanics.
The only unit within the Deakin
Volcanics, the Mugga Mugga Porphyry Member, to be named was considered by Opik to be an intrusive sill, it is now considered to be extrusive, possibly a lava, near the base of the Deakin Volcanics. The Deakin Volcanics are overlain, in places conformably, in others disconformably, by the Laidlaw Volcanics.
The Laidlaw Volcanics is formed
essentially of one very thick rhyodacite ignimbrite cooling unit, which extends some 95 km along strike, and reaches a thickness of up to 300 m. Lithic fragments are rare.
The presence of fresh biotite in many outcrops
of the Laidlaw Volcanics has enabled a Rb/Sr age of 419 +_ 1.6 m.y. to be obtained, which, since the stratigraphic age of the Volcanics is closely controlled as earliest Ludlow in the Yass area, provides an excellent point on the geological time scale (Wyborn et al., in prep.). The third unit in the Laidlaw Suite is the Swamp Creek Volcanics. These crop out some 20 km west of Canberra, overlie disconformably the Walker Volcanics, and consist of essentially air fall tuffs, at times agglomeratic, with minor ignimbrites.
Their relationship to the other two
units of the Laidlaw Suite is made uncertain by faulting, however it is probable that they are laterally equivalent to the Deakin Volcanics, and may represent material deposited close to the main volcanic pile from which the Deakin Volcanics were derived.
STOP 1.1
Agglomeratic tuff within Ainslie Volcanics. Canberra 1:100 000 sheet.
G.R, 956937
Boulder outcrops of an almost monomict agglomeratic tuff with little compositional difference between clasts (up to 30 cm across) and matrix. Based on the outcrop alone, at least four modes of deposition are possible, 1. an ignimbrite, 2. air fall tuff, 3, brecciated base or top of lava flow, or 4. pyroclastic debris flow.
83
Local mapping shows the unit to be only local in extent, being limited between the two gullies, and this, accompanied by the lack of bedding suggests that the last alternative may be the most likely.
STOP 1.2
Dacite within Ainslie Volcanics. 1:100 000 sheet.
G.R. 956933 Canberra
A fresh boulder, plus weathered outcrops showing apparent bedding, of dacite within the Ainslie Volcanics.
The dacite contains phenocrysts
of quartz, plagioclase (albite), biotite, cordierite and garnet. fragments are fairly rare, as is possible pumice.
Lithic
The rock may represent
either an airfall or ignimbrite tuff, depending on the nature of the apparent bedding in the weathered outcrops.
STOP 1.3
Narrabundah Ashstone Member of Canberra Formation. Canberra 1:100 000 sheet.
G.R. 979916
A new roadcut exposing a section through most of the Narrabundah Ashstone.
The Ashstone is the oldest named "volcanic" unit in the Canberra
area and is a member of the late Wenlockian Canberra Formation.
The term
Ashstone appears something of a misnomer, at least here, since much of it appears to be a volcanoclastic arenite.
It is underlain at this locality
by fossiliferous marine mudstones in the creek, and is also overlain by marine sediments.
Emplacement of the Narrabundah Ashstone appears to have been by
submarine mass flow;
presumably a near shore body of sand became unstable
and flowed downslope as a turbidity flow, depositing a thick, unbedded arenite, and then finer silt- and mud-sized material was deposited from the suspended material left behind the main flow.
Subsequent small flows then produced
the thin well-bedded units overlying the main "ashstone".
Its volcanoclastic
composition does however indicate the presence of volcanism in the region before the eruption of the Ainslie Volcanics started.
STOP 1.4
Mt Painter Volcanics.
G.R. 937864.
Canberra 1:100 000 sheet.
Large boulders removed from the nearby road cut are typical of the Mt Painter Volcanics.
These volcanics were for long considered to be
intrusive but are now considered to be of ignimbritic origin.
Features of
the unit are the high phenocryst content (up to 80%), the abundance of lithic
84
fragments, and the relative abundance of garnet and cordierite. Fiamme are particularly common at this locality.
STOP 1.5
Mugga Porphyry.
G.R. 927862.
Canberra 1:100 000 sheet.
The Mugga Porphyry is the second important volcanic unit in the Canberra area once considered to be intrusive but now thought to be extrusive.
It is now regarded as a member low in the Deakin Volcanics.
The Mugga Porphyry is a rhyodacite with phenocrysts of quartz, plagioclase, sanidine, biotite and hypersthene forming about 40% of the rock.
The
most noticeable feature is the lack of virtually any inclusions or foliation.
The mode of emplacement is still uncertain, possibly it may
be a lava since it thins rapidly and disappears about 2 km to the NW of this stop.
STOP 1.6
Airfall tuff in Deakin Volcanics. Canberra 1:100 000 sheet.
G.R. 944784
A new road cutting with good exposures of dominantly airfall tuff.
The rock is well-bedded, very poorly sorted, with clasts (which are
often angular) up to 5 cm (though usually less than 2 cm) across.
An
alternative mode of deposition, waterlain sediments, can be discounted because of the very poor sorting and presence of angular clasts.
The
lower beds in the middle part of the cutting appear to be unbedded, and may represent a mud flow.
STOP 1.7
Autobrecciated lava in Deakin Volcanics. Canberra 1:100 000 sheet.
G.R. 938771
Roadcut about 1 km south of previous stop.
A rather weathered
section which shows two zones of brecciation thought to represent autobrecciation at either the top or bottom of lava flows.
The southern zone
has clasts up to 50 cm across in a red ash matrix while the northern zone has a ?rhyodacitic matrix, similar to the clasts.
85
STOP 1.8
Coarse tuff in Laidlaw Volcanics. Canberra 1:100 000 sheet
G.R. 862776,
Good outcrops in the bed of the Murrumbidgee River.
The bulk of
the Laidlaw Volcanics is a rather featureless grey rhyodacite, however locally, bedded airfall tuff and agglomerate are found. the most interesting of these.
This locality is
A variety of rock types are present,
including fine and coarse airfall tuff and ignimbrite.
An unusual feature
is the variety of rock-types present in the clasts, and also the degree of rounding of some clasts.
STOP 1.9
Ignimbrite flows and interbedded fluviatile sediments in Deakin Volcanics. G.R. 876891, Canberra 1:100 000 sheet. This excellent, though rather weathered, roadcut exposes a
sequence of interbedded fluviatile sediments and ignimbrite flows almost at the base of the Deakin Volcanics.
Features to note include the irregular
top of the first main ignimbrite, with what appear to be cooling joints infilled with sediment, and the disturbed layer in the sediments at the base of the second flow.
Features such as these have undoubtedly contributed
to the past interpretation of porphyries in the Canberra area as intrusive when these features have been seen in isolated small exposures.
STOP 1.10
Dacite in the Walker Volcanics. Brindabella 1:100 000 sheet.
G.R. 775978,
Outcrops in the bed of the Murrumbidgee River.
This is part of the
type section of the Walker Volcanics, and is typical of much of the unit. Massive reddish-purple dacite, with garnet xenocrysts forms the most common rock type and presumably represents strongly welded ignimbrite flows. Bedded airfall tuffs are often found however, though bedding may be rather indistinct, as at this locality.
STOP 1.11
Contact of Walker and Swamp Creek Volcanics. Brindabella 1:100 000 sheet.
G.R. 763993
The contact between the Walker Volcanics and the Swamp Creek Volcanics is exposed in a small pit near the base of an electricity pylon, Weathered purple dacite of the Walker Volcanics is overlain by a bedded ashstone,
86
the Taupaulin Creek Ashstone which is the basal member of the Swamp Creek Volcanics.
This is followed by coarse, airfall tuff in which pink sanadine
crystals are prominent.
Bedding is present in much of the Swamp Creek
Volcanics but is often rather indistinct.
STOP 1.12
Dacite and limestone in the Paddys River Volcanics. G.R. 763883, Brindabella 1:100 000 sheet. The Paddys River Volcanics are the oldest volcanics in the Cotter
area, and are thought to broadly correlate with the Ainslie Volcanics.
The
outcrops of dacite in the river illustrate the problem faced deciding if a volcanic rock formed in a submarine or subaerial environment.
This dacite
is presumably submarine, since it is very close to a large limestone lense, however it is similar to many dacites in the subaerial Ainslie Volcanics.
STOP 1.13
Rhyodacite in Laidlaw Volcanics. 1:100 000 sheet.
G.R. 784884, Brindabella
Typical grey rhyodacite of the Laidlaw Volcanics exposed in a small roadside quarry.
The Laidlaw Volcanics are composed almost exclusively of
this rhyodacite, and appear to have formed essentially as a single cooling unit up to 300 m or more thick and extending at least 95 km. this locality have been used for palaeomagnetic work at ANU.
Samples from
87 DAY 2
5th December 1980 SILURIAN VOLCANIC ROCKS OF THE YASS AREA
INTRODUCTION Not unexpectedly, much less is known about the Silurian felsic rocks of the Yass area than those around Canberra, and currently, only two units are recognized, the older Hawkins Volcanics, and the Laidlaw Volcanics.
Both volcanic units, and the sedimentary Yass Formation between
them, have had a chequered nomenclature in the past, and details can be found in Cramsie et. al. (1978) and Owen and Wyborn (1979).
The names are
used here in the sense of Owen and Wyborn (1979). The Hawkins Volcanics, which are part of, and provide the name for, the Hawkins Suite, are closely similar in mineralogy and range of rock types to the members of the Suite in the Canberra area.
So far, no attempt
has been made to subdivide the Hawkins Volcanics, however some initial reconnaissance traverses has indicated that this may ultimately be possible. A feature of the Hawkins Volcanics is the increasing abundance of garnet upwards through the sequence, a feature also of the Hawkins Suite in the Canberra and Cotter areas. The Laidlaw Volcanics of the Yass area (which is the type area for the unit) are essentially identical in lithology to their occurrence further south, around Canberra, and are mostly composed of massive ignimbrite, though around Yass township bedded waterlain and airfall tuffs occur at the base and top of the unit.
The Deakin Volcanics, which underlie the Laidlaw
Volcanics in the Canberra area thin northwards and disappear midway between Yass and Canberra. STOP 2.1
Dacite ignimbrite in Hawkins Volcanics. Gunning 1:100 000 sheet.
G.R. 830318
Roadside boulders show a massive dacite which contains cordierite but no garnet.
Good examples of fiamme are also present.
The rock is
assumed to be an ignimbrite rather than airfall tuff since bedding is absent.
88
STOP 2,2
Dacite ignimbrite in Hawkins Volcanics, Gunning 1:100 000 sheet.
G.R. 841280
Outcrops of dacite ?ignimbrite at a stratigraphically higher level than the previous stop.
Garnet xenocrysts are relatively common.
The rock is similar in many respects to the Mt Painter Volcanics, particularly in the high proportion of phenocrysts (about 80%), and occupies a similar stratigraphic level, near the top of the Hawkins Suite, but lacks the abundant lithic fragments of the Mt Painter Volcanics.
STOP 2.3
Rhyodacite of Laidlaw Volcanics. 1:100 000 sheet.
G.R. 759317, Yass
Some rather unimpressive outcrops of rhyodacite ignimbrite, typical of the Laidlaw Volcanics are remarkable for the beautiful euta&itic layering in the groundmass, visible in thin-section.
ST0P2.4
Coarse tuff and agglomerate in Laidlaw Volcanics. G.R. 750310, Yass 1:100 000 sheet. The Yass 1:100 000 geological map (Cramsie et al., 1975) shows
a large (20 sq km), roughly circular area of volcanic breccia, agglomerate and tuff within the Laidlaw Volcanics some 12 km south of Yass.
This unit
was subsequently suggested (Cramsie et al., 1978) to be a volcanic centre for the Laidlaw Volcanics, since it appeared to have gradational boundaries with typical Laidlaw Volcanics.
This conclusion is supported here though
the area of outcrop appears much smaller, possibly 10-12 sq km.
Much of
this area is formed by rock similar to this stop, that is, massive coarse tuff and agglomerate with the majority of clasts being of volcanic origin, though clasts of sedimentary rock are also common.
The rock is unsorted,
usually massive, with angular clasts up to 25 cm across or greater. Locally, moderate to well-bedded airfall tuff is present. Ths similarity with parts of the Swamp Creek Volcanics is worth noting.
89
STOP 2.5
Reworked tuffs at top of Laidlaw Volcanics. Yass 1:100 000 sheet.
G.R. 724432
This section in the Yass River is in the upper part of the type section of the Laidlaw Volcanics.
It shows a varied sequence of reworked
tuff together with some possible air-fall or ignimbritic tuff. More massive ignimbrite flows occur further upstream.
REFERENCES FOR DAYS 1 AND 2 CRAMSIE, J., POGSON, D.J., and BAKER, C.J., 1975: Sheet.
Yass 1:100 000 Geological
Geol. Surv. N.S.W. 1978:
1:100 000 Sheet 8628. OPIK, A.A., 1958:
Geology of the Yass
Geol. Surv. N.S.W.
Geology of the Canberra City district.
Bur. Miner.
Res. Bull. 32. OWEN, M.,
§
WYBORN, D., 1979:
Geology and Geochemistry of the
Tantangara and Brindabella 1:100 000 sheets.
Bur. Miner. Res. Bull. 32.
WYBORN, D., OWEN, M., McDOUGALL, I., and COMPSTON, W., in prep.:
The
Laidlaw Volcanics, a Late Silurian point on the geological time scale.
90
DAY 3
5th December, 1980
THE LOWER DEVONIAN MERRIONS TUFF
SUMMARY The Merrions Tuff is a formation of volcaniclastics and conformable porphyritic igneous horizons, presently outcropping over 1,850 sq. kms. within the deformed, regionally metamorphosed, flyschoid fill of the SiluroDevonian Hill End Trough (Fig. 1). Texturally, mineralogica]ly and chemically, the igneous horizons appear to have been glassy andesites/dacites and rhyodacites of calc-alkaline affinity.
On chemical variation diagrams they form a continuous series with
the volcaniclastics.
Three conformable horizons have been recognized.
are grossly tabular and have lobate outlines (Fig. 2).
They
Their coherent,
variably vesicular character and their association with subaqueously emplaced mass-flow deposits, suggests that they were lavas that were both erupted and emplaced in relatively deep water.
Their apparent mound-like
morphology appears to have affected the thickness of succeeding units. They are more extensive than compositionally equivalent, subaerial silicic lavas.
Their coherent character may be characteristic of silicic lavas
erupted under the higher environmental pressures of subaqueous environments. High ambient pressures may inhibit exsolution of volatiles and so maintain flow mobility. The volcaniclastics are classical crystal tuffs:
they are
overwhelmingly closed framework aggregates of unabraded crystals and fragments of volcanic quartz, plagioclase and K-feldspar.
Matrix is
subordinate and vitriclasts and recognisable shards are minor.
The gross
similarity between the clastic mineral grain assemblages and the phenocryst assemblages of the lavas, and the continuous chemical series defined by the lavas and the volcaniclastics, suggest that the crystal tuffs were derived from magmas compositionally similar to the lavas.
Furthermore specimens
of both the volcaniclastics and the lavas were used to define a tight Rb/Sr isochron of 395 ± 32 m. years, suggesting that the volcaniclastics and lavas are penecontemporaneous and that the volcaniclastics were deposited rapidly after explosive fragmentation i.e. they were not reworked and mixed with, or contaminated by, older terrigenous detritus.
The crystal-tuffs are
however very rich in framework grains relative to fine matrix (?ash) 0 r fine grained volcanic rock fragments.
Few, unfragmented lavas with
91
equivalently high phenocryst proportions are documented, suggesting that in the Merrons Tuff a significant proportion of the groundmass of the erupting magma was lost, most likely during eruption and explosive fragmentation. The volcaniclastics are dominantly arenites organized into very thick (metre to tens of metres) sedimentation units that are regionally extensive.
Sedimentation units are massive and show continuous size
grading only where sedimentation units are relatively thin (< 2m.).
More
commonly sedimentation units are not graded or graded only in the upper parts.
Sedimentation units are often juxtaposed without intervening
pelitic horizons.
Sedimentary structures present include diffuse
layering,
outsize rip-up clasts, minor channelling, and rare flame structure and dish structure (Fig. 3 ) .
The characteristics of the sedimentation units
suggest emplacement by M cold state", large scale, subaqueous mass-flows. Normal or continuous size grading suggests that turbulent suspension was the dominant grain-support/flow mechanism.
Lack of continuous size grading
implies that dispersive pressure (inertial), involving a high degree of grain collisions, and the buoyancy effect of the interstitial fluid may also have been important grain-support/flow mechanisms.
Regional facies relationships
suggest emplacement within a deep marine basin.
Although the high sand-to-
shale ratio and the non-graded to partly graded aspect of the thick Merrions Tuff sedimentation units may suggest emplacement in inner-fan valley or mid-fan channel subenvironments of submarine fan systems, the laterally continuous and homogeneous character of the formation regionally, mitigates against this.
A relatively even basin-floor surface is preferred.
The Merrions Tuff is the structural-stratigraphic marker of the flysch-like fill of the Hill End Trough and is grossly tabular in form (Figs. 1, 4, 5 ) .
Internal vertical and lateral heterogeneities allow
subdivision into members.
Although some members are regionally extensive,
others are not, so leading to a complex internal stratigraphy (Figs. 4,
5).
Identification of regionally extensive time planes and analysis of the timestratigraphy shows that the base of the Merrions Tuff is diachronous, suggesting lateral facies equivalence with the enclosing, more pelitic flyschoid successions.
Although mesoscopic sedimentary structures (such as
sole structures) are rare or not exposed, analysis of the parameters: spatial distribution of members, variation of and within members of their shape, thickness, grainsize, sand-to-shale ratios, numbers of sedimentation units, distribution of vitriclasts, demonstrates that the Merrions Tuff was not derived from a single source and a single eruptive phase, but from several sources which were variously active at different times.
Furthermore,
92
through time there appears to have been a shift in the direction of dominant influx of basin fill, from the west through to the south, to the southeast and finally the east (Fig- 6).
Depositional patterns were controlled by a
changing basin-floor topography which was particularly influenced by the emplacement of the very thick member B lava.
The effect of this flow was to
displace the northwest-southeast trending basin axis existing at the beginning of the history of the Merrions Tuff to the east.
REFERENCES
CAS, R.A.F., 1976: setting.
The Merrions Tuff:
its genesis and palaeogeographic
Unpub. Ph.D. Thesis, Macquarie University, 265 p.
:
Basin characteristics of the Early Devonian part of the
Hill End Trough based on a stratigraphic analysis of the Merrions Tuff.
Jl. Geol, Soc. Aust. 24, p.381-401.
:
Silicic lavas in Palaeozoic flysch-like deposits in New
South Wales, Australia: f1ows.
Behaviour of deep subaqueous silicic
Geol. Soc. Amer. Bull., v. 89, p.1708-1714.
1979:
Mass-flow arenites from a Palaeozoic interarc basin, New
South Wales, Australia:
Mode and environment of emplacement.
Jour. Sed. Petrology, v.49, p.29-44.
CAS, R.A.F., FLOOD, R.H., and SHAW, S.E., 1976: metric ages.
Search, v.7, p.205-207.
Hill End Trough:
new radio-
93
Merrions
FIG.
1.
Tuff
[+
+ | Carboniferous
OUTCROP PATTERN OF THE MERRIONS T U F F ,
SECTIONS AND LOCATION OF STOPS ON THIS
TRIP.
Plutons
LOCATION OF STRATIGRAPHIC
94
Member B(d lavas (oldest) /
Member H lavas (youngest)
MUDGEE v>
/ (I50)\. -|0O
•200
'•s^200 ' '50
100.
Member B(2j u lavas (intermediate age)
FIG. 2.
(a) PLAN VIEW SPATIAL RELATIONSHIPS BETWEEN THE THREE LAVA UNITS
OF THE MERRIONS TUFF.
THICKNESS CONTOURS IN METRES.
(b) SEQUENCE OF
EMPLACEMENT OF THE THREE LAVA UNITS, SHOWN SCHEMATICALLY.
95
M s massive texture gc = coarse fraction a n d / o r coarse fraction frequency grading in massive zone g = total size grading in all or part of massive zone I = diffuse l a m i n a t i o n / t h i n bedding in massive zone x - cross lamination/bedding in granular sediment zones con = convolute lamination d s h = d s h structure P = pelitic zone including laminated, t h i n l y - b e d d e d , ( c r o s s - l a m i n a t e d ) , massive pelite A - gravel size vitriclasts @ = frequency
FIG. 3.
COMBINATIONS OF DIFFERENT SEDIMENTARY STRUCTURES AND TEXTURES
WHICH MAKE UP DIFFERENT SEDIMENTATION UNIT TYPES. PREDOMINATES. ZONES IN AN
NO SCALE IMPLIED.
MASSIVE TEXTURE
SUBSCRIPT NUMBERS RELATE TO DIFFERENT
EXPANDED BOUMA SUCCESSION.
FIG. 4.
SEE NEXT PAGE.
FIG. 5.
SCHEMATIC STRATIGRAPHIC PROFILES OF THE MERRIONS TUFF.
REFER TO FIG. 4.
96
PERSPECTIVE •
Elevated view from south , ground dimensions distorted; vertical not.
Measured Section No. Member 6 clastics 8 regional matrix rocks
Time Line
Merrions Tuff inferred
-t6 Member E plastics
t5
Member J pelites Member H lavas lincl. I clastics)
t4
FIG, 4 . TUFF.
I
Member D clastics T3 Member P clastics
VERTICAL SCALE
Member M clastics I Member L I clastics I Member C pelites
H O R I Z O N T A L SCALE -variable -dimensions shown
THREE DIMENSIONAL' STRATIGRAPHIC CONFIGURATION OF THE MERRIONS TIME PLANES ARE ALSO REPRESENTED.
97
FIG. 6.
DEPOSITIONAL HISTORY OF THE MERRIONS TUFF.
SHOWN ARE INFERRED
FLOW PATTERNS (LARGE ARROWS), INFERRED TOPOGRAPHIC LOWS ( 'K ) AND HIGHS ( 4 ), AND INFERRED PALAEODOWNSLOPE DIRECTIONS (SMALL ARROWS).
93
STOP 1:
Stratigraphic section 1, type section of the Merrions Tuff, Turon
River, Turondale, N.S.W. (Fig. 7).
G.R. 266-7/928, Bathurst 1:250,000 Sheet SI 55-8
Chlorite zone metamorphic grade. In this section, the base of the Merrions Tuff abruptly overlies
thinly bedded pelites and sandstones of the Waterbeach Formation.
The top
of the formation grades rapidly into the lithic sandstones and slates of the Cunningham Formation.
The section consists of very thick, massive
sedimentation units of crystal tuff, parabreccia and silicified pelites and a middle interval of lava, which is in part brecciated.
This lava (member H)
is the youngest of the three lava units in the formation.
The older two do
not occur in this section nor in any of the sections in a NNW direction from here (see Figs. 4 and 5).
Vitriclasts are particularly abundant in this
section. STOP 2:
Stratigraphic section 10, Winburndale Rivulet, N.S.W.
Bathurst 1:250,000 Sheet SI 55-8 (Fig. 8).
G.R. 254-5/893
Biotite zone metamorphic grade.
In this section, the base of the Merrions Tuff is not as clear cut as in the type section.
There is probably an interdigitational relationship
with Waterbeach Formation facies sediments.
Vitriclasts are less abundant
in the volcaniclastics than in stratigraphic section 1 and the volcaniclastics are generally finer grained apart from several breccia horizons.
Two lava
units, both older than the one in the Turon River section occur.
At one
locality there is a good exposure of the contact between the base of the lowest lava and the underlying silicified pelite.
Correlations between this
section and the type section are shown in Figs. 4 and 5.
In Fig. 5,
section 11 is essentially the same as section 10 and lies a little to the north of section 10 so that the same correlations apply.
99
THE
Modal Analysis (Repr of
Unifs 16-20)
Volcanic Quartz
19
MERRIONS TUFF
(Type Section on the Turon River eost of Sofala,NS.W)
Plagioclase (Albite) 5 6 0 K-felspar Volcanic RF.
Turondaf
Chloritized porphyry boulders in quartzose ptogioclase arenite
0 2
^
7 5
Mafrix/Cement
34 4 100.0
^BATHURST
Crudine Group
Porphyry specimen shows relict perlitic texture
Modal Analysis (Repr of Units 4 - 1 3 ) Base of porphyrv
Volcanic Quartz
39 3
Plagioclase (Albite) 19.9 K-felspar Porphyry boulders in sandy
L b o p O o P g • Mottled
~
28.3
Volcanic R F.
2 .3
Matrix / Cement
10 2
/ -
^ < r C h o n n e l - fill , \ P a r a b r e c c i a of , \ glassy V R F _ _ E _ _ L
._•. -
sandy pelife _
Parabreccia' as Channel Fill
0 ^ .
Parabreccia^x * Seel U n i t ( 4 ) N (Closts: L / s , p e l i f e , \ Glossy volcanic R F )
Modal Analysis
Diffuse
Volcanic Quartz
0
Plagioclase( Albite) 6 0 6
Plagioclose Arenite
K - felspar
START HERE
0
Volcanic R.F
2.4
Matrix/Cement
370
LEGEND Siltstone / Pelife
S3
&
Chert Interbedded L u t i t e / C h a r t
Thinly Interbedded or Laminated Arenite and Pelife
Arenite
STOP 1.
Graded Strata
Erosional Base
Chloritized Glassy Porphyry Boulders G o O o
°/)
Docite Porphyry
FIG. 7.
Dacite Porphyry Boulders
Chloritized Glassy Volcanic Rock Fragments
Limestone
Pelife
TURON RIVER.
Boulders
Intraclasts
m s
Diffuse Lamination /bedding Inferred Bedding Contact
SKETCH MAP OF STRATIGRAPHIC SECTION 1,
THE TYPE SECTION, AND ACCURATE MEASURED SECTION (scale in metres gives true thickness, not ground dimensions).
-/
100
CAVA UNIT
B
B
2
I
SPECIMEN MU4644 MU4653 64.50 63.06
Si02 Ti02 AI2O3 Fe203
.60 .61 14.48 14.95 1.78 1.97
FeO MnO MgO CaO Na20 K2O
2.62 .14 1.74 3.32. 2.16 5.39
2.82 .10 1.84 3.63 4.59 3.36
.18
.19
P205 TOTAL '' KpO/NapO
CUWN1HGHHM FORMATION
97.11 96.92 2.52
.75
| wrterberch"
FQRhwnoiTI
T.N.
FIG. 8.
STOP 2.
WINBURNDALE RIVULET.
SKETCH MAP OF STRATIGRAPHIC
SECTION 10, AND ACCURATE MEASURED SECTION (scale in metres gives true thickness, not ground dimension).