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LATE PROTEROZOIC TO DEVONIAN SEQUENCES OF SOUTHEASTERN AUSTRALIA, ANTARCTICA AND NEW ZEALAND AND THEIR CORRELATION

Authors: A. V. Brown, R. A. Cooper, K. D. Corbett, B. Daily, G. R. Green, G. W. Grindley, J. Jago, M. G. Laird, A. H. M. VandenBerg, G. Vidal, B. D. Webby and H E. Wilkinson Editors: R. A. Cooper and G. W. Grindley

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LATE PROTEROZOIC TO DEVONIAN SEQUENCES OF SOUTHEASTERN AUSTRALIA, ANTARCTICA AND NEW ZEALAND AND THEIR CORRELATION

Authors A.V. Brown R.A. Cooper K.D. Corbett B. Daily G.R. Green G.W. Grindley J. Jago M.G. Laird A.H.M. VandenBerg G. Vidal B.D. Webby H.E. Wilkinson

Editors R.A. Cooper and G.W. Grindley 1982

SPECIAL PUBLICATION NO. 9 Geological Society of Australia, Inc.

Publication of the International Geological Correlation Program PROJECT 7 SOUTHWEST PACIFIC BASEMENT CORRELATION

ISBN 0 909869 21 9 ISSN 0072-1085

Authors' addresses: R.A. Cooper, G.W. Grindley, M.G. Laird1 K.D. Corbett, A.V. Brown, G.R. Green 2 B. Daily3 J. Jago4 B.D. Webby5 H.E. Wilkinson, A.H.M. VandenBerg6 G. Vidal7 1

New Zealand Geological Survey, Lower Hutt and Christchurch 2 Geological Survey, Department of Mines, Hobart, Tasmania Department of Geology, University of Adelaide, Adelaide, S.A. 4 South Australian Institute of Technology, Ingle Farm, S.A. s Department of Geology and Geophysics, Sydney University, N.S.W. 6 Department of Minerals and Energy, Bendigo and Melbourne, Victoria ? Dept of Historical Geology and Palaeontology, Lunds Universitet, Lund, Sweden 3

CONTENTS ABSTRACT ... 1.

INTRODUCTION 1.1 Time divisions 1.2 Aim and organisation 1.3 Authorship responsibility ... 1.4 Acknowledgements

REGIONAL SEQUENCES - SOUTH AUSTRALIA ... 2.1 Yorke Peninsula ... 2.2 Mount Lofty Ranges, Fleurieu Peninsula, and Dudley Peninsula (Kangaroo Island) 2.3 North coast of Kangaroo Island 2.4 Flinders Range ... 2.5 Tectonic history, palaeogeography ...

WESTERN NEW SOUTH WALES... 3.1 Barrier Range ... ... ... 3.2 Bancannia Trough 3.3 Mt Wright Volcanic Belt ... 3.4 Gnalta Shelf 3.5 Relation to Central-Western and Eastern New South Wales ...

ANTARCTICA ... 4.1 CentralTransantarcticMountains ... 4.2 Northern Victoria Land ... 4.3 Tectonic history and palaeogeography

TASMANIA 5.1 Precambrian basement rocks 5.2 Smithton Trough and King Island ... 5.3 DundasTrough ... 5.4 Dial Range Trough , ... 5.5 Fossey Mountains Trough and Beaconsfield ... 5.6 Adamsfield Trough 5.7 Ordovician and Siluro-Devonian post-trough sequences 5.8 Mathinna Beds of Eastern Tasmania 5.9 Tectonic, metamorphic and igneous history ...

VICTORIA 6.1 Glenelg Sedimentary Belt - western part 6.2 Glenelg Sedimentary Belt - eastern part 6.3 Stawell Sedimentary Belt ... 6.4 Bendigo Sedimentary Belt... 6.5 Heathcote Belt ... 6.6 Melbourne Trough Belt ... 6.7 Mount Wellington and Waratah Bay Belts 6.8 Eastern Victoria ... 6.9 Tectonic history and palaeogeography

...

NEWZEALAND ... ... ... 7.1 Western Sedimentary Belt... ... 7.2 Eastern Sedimentary Belt ... ... 7.3 Central Sedimentary Belt ... ... 7.4 Fiordland ... ... ... 7.5 Campbell Plateau ... ... 7.6 TasmanMargin ... ... ... 7.7 Palaeogeography; tectonic, igneous andmetamorphichistory ... ...

... ... ... ... ... ... ...

48 48 50 50 51 52 52

...

MICROFOSSIL STUDIES 8.1 New Zealand ... 8.2 Tasmania ... 8.3 Antarctica ... 8.4 General ...

... ... ... ... ...

55 55 55 56 56

PRINCIPAL INTER-REGIONAL CORRELATIONS AND GEOTECTONIC EVENTS ... ... ... ... 9.1 Age and nature of the Precambrian Basement ... 9.2 Late Proterozoic sedimentary cycle ... ... ... 9.3 Early to Middle Cambrian volcanics and ultramafics ... 9.4 Middle Cambrian - Early Ordovician tectonic, intrusive, metamorphic, and related sedimentary events ... 9.5 Ordovician clastic sedimentation ... ... ... 9.6 Late Ordovician - Early Silurian tectonic, metamorphic, igneous and sedimentary events ... 9.7 Late Silurian to Early Devonian tectonic, metamorphic, igneous and sedimentary events ... 9.8 Middle - Late Devonian tectonic, metamorphic and igneous events ... ... ... ... 9.9 Bass Strait structure, palaeomagnetics and Tasmania - Victoria relationships ... ... ...

... ... ... ...

57 57 59 61

... ...

64 66

...

PALAEOTECTONIC/PALAEOGEOGRAPHIC RECONSTRUCTION 10.1 Problems in Inter-continental reconstructions ... ... 10.2 Recommendations for further study ... ... ...

72 72 72

APPENDIX - NOTES ON CORRELATION CHART... South Australia ... ... ... ... Tectonic, igneous and metamorphic events ... Western New South Wales ... ... ... Tectonic and metamorphic events ... ... Antarctica ... ... ... ... ... Tectonic, igneous and metamorphic events ... Tasmania ... ... ... ... ... Tectonic, igneous and metamorphic events ... Victoria ... ... ... ... ... Tectonic, igneous and metamorphic events ... New Zealand ... ... ... ... ... Tectonic, igneous and metamorphic events ...

10.

REFERENCES

...

... ... ... ... ...

... ii

... ... ... ... ...

...

... ... ... ... ... ... ... ... ... ... ... ... ...

74 74 74 75 75 76 78 79 82 82 86 87 88

...

Introduction

ABSTRACT The scientific results of International Geological Correlation Program, Project No.7 (Southwest Pacific Basement Correlation) are presented and discussed. The principal objectives of the correlation project have been to enable Australian and New Zealand geologists to jointly examine critical late Precambrian to Devonian rock belts in the field in New Zealand, Antarctica, South Australia, western New South Wales, Victoria and Tasmania as a basis for comparison and correlation of sequences. Thirty representative stratigraphic columns, covering this sector of Gondwanaland, show detailed biostratigraphic, sedimentary, igneous, met amorphic and tectonic information for each region. The geological history of each region is described and discussed fully in the accompanying text, and additional notes on each column are given in an appendix. Generalised geological maps are provided for the regions discussed. The first study (Section 8) of late Proterozoic (Vendian) to Cambrian acritarch assemblages extracted from rock units in New Zealand, Tasmania and northern Victoria Land, Antarctica, shows the promise of this group for correlating many hitherto unfossiliferous sedimentary sequences. Major geotectonic, sedimentary, igneous and metamorphic events are correlated. It is obvious that all the regions shared an integrated geological history throughout most of the interval and must be considered as parts of the same geotectonic province. However, significant inter-regional comparisons and contrasts exist that are not predictable from the late Mesozoic configuration of the region determined from sea-floor spreading. These 'anomalies' provide a means of testing proposed reassemblies of the continental fragments in the Palaeozoic. Further studies in critical regions of sedimentary facies, igneous rock geochemistry, radiometric dating, biostratigraphy, palaeomagnetism and regional structural analysis are required before Palaeozoic reconstructions can be attempted with any degree of confidence.

1. INTRODUCTION This publication presents results of studies undertaken by International Geological Correlation Program Project 7 'Southwest Pacific basement correlation' (leaders R.A. Cooper and G.W.Grindley). The purpose of the project was to enable New Zealand and Australian geologists to jointly examine critical late Proterozoic to mid Palaeozoic rock belts and sequences in the field in New Zealand, Antarctica and SE Australia (Fig. 1) areas which together are thought to have comprised a single sector of early Palaeozoic Gondwanaland - as a basis for comparison and correlation. A comparatively detailed correlation of sequences has been prepared and is presented here (Fig. 2). During the last decade, numerous palaeotectonic or palaeogeographic models of the region have been proposed (references listed in Laird et al., 1977, Grindley & Davey , 1982). It is not our intention here to review previous models or to propose a new model, but rather to present data on which detailed comparisons of the various continental segments, and palaeogeographic models of the region, must be based. The time interval studied - late Proterozoic to Devonian was chosen because it coincides with a natural depositional-orogenic cycle throughout much of the southwest Pacific. During the course of the Project, an extensive sampling programme for extraction of insoluble, organic-walled microfossils was undertaken by one of us (Vidal) in an attempt to determine the age of some poorly known units, mainly those thought to be of late Proterozoic or Early Cambrian age. The results of the study have been incorporated in our correlations, and are briefly summarised below.

Introduction

. . SOUTH 1 Australia!

fWESTERN.+ NSW. :.:.;. \.

TASMANIA^

ZEALAND CHATHAM RISE

SOUTH \ TASMANN y \ RISE

CAMPBELL PLATEAU

KJ>- bore hole penetrating' to basement /

vV1. NORTHERN / . VICTORIA v/LAND /

SOUTHERN .VICTORIA V& LAND^ SHELF

MARIE BYRD Sj-AND

.'CENTRAL t TRANSANTARCTIC^^^^'.V. . . .. . MOU NTAINS • • .'

'S&'&A NT A R C f IC A Fig. 1 Southwestern Pacific region showing location of areas discussed in this publication (in black). One thousand metre isobath also shown. Seafloor spreading axis (mid ocean ridge) marking the boundary of the Antarctic Plate is shown together with the now extinct spreading axis between Australia and New Zealand (active 80-60 Ma ago). Inset shows late Cretaceous positions of Australia, Antarctica and New Zealand (after Crook and Belbin, 1978).

Time divisions

1.1 Time divisions Time, and time-stratigraphic, divisions used here (Fig. 2) are those in general use in Australasia. The oldest Precambrian rocks in the region are assigned to the Archaean, that is, older than about 2300 Ma (Webb & Thomson 1977). Proterozoic spans from Archaean to Cambrian and the younger part of the time scale shown on the correlation chart has been constructed from various sources. The Silurian - Devonian (at 410 Ma) and Ordovician - Silurian (at 435 Ma) boundaries follow the recommendation of Spjeldnaes (1978), who has relied heavily on radiometric dating of volcanics interbedded with early Silurian graptolitic shale horizons in Alaska (Lanphere et al., 1977). More recently, Ross et al., (1978) provided numerous fissiontrack dates on zircons from bentonitic tuffs in Ordovician and Silurian sediments in Britain, well dated by graptolites. Compston (1979) has pointed out the agreement between these new dates and previous dates obtained by the Rb-Sr method on sediments and K-Ar dates on hornblende from volcanics. The scale adopted, however, differs appreciably from that recommended by Armstrong & McDowall (1975) - (416-446 Ma for the Silurian) and by Gale et al., (1979) - (418 Ma for the Ordovician - Silurian boundary). The Devonian - Carboniferous boundary is taken at 360 Ma, following recent dating of Upper Devonian granitic rocks in southeastern New South Wales close to the Victoria border (Fergusson et al., 1979). Dating of series boundaries within the Victorian Devonian (Table 1) is also becoming more refined using the palaeontological evidence (marine fossils in the Early Devonian and freshwater fish faunas in the Late Devonian). The Ordovician - Cambrian boundary still provides the greatest uncertainty. A discrepancy of 24 Ma between Armstrong & McDowall (1975) - 509 Ma and Cowie & Cribb (1978) - 485 Ma is still not resolved. Gale et al. (1979) have suggested 490 ± 9 Ma as a maximum age for the base of the Tremadoc and 482 Ma for the Tremadoc - Arenig boundary. They also suggest an age of 418 Ma for the base of the Silurian based on a single Rb-Sr isochron on rhyolite flows near the top of the Ordovician, but these ages may be affected by nearby Devonian granite. We have provisionally chosen a figure of 500 Ma for the base of the Ordovician (Tremadoc) and 485 Ma for the base of the Arenig. These dates fit best with the geology of the region, especially with the radiometric data on the Delamerian and Granite Harbour Intrusives and the widespread development of thick Tremadocian quartz-greywacke flysch. The age of the base of the Cambrian (including the non-trilobite-bearing Tommotian Stage) is taken at 575 Ma following Armstrong & McDowall (1975). However, Cowie & Cribb (1978), relying heavily on Russian K-Ar dates on glauconites, have proposed 590 Ma for this boundary and 570 Ma for the base of the Lower Cambrian above the Tommotian Stage. The age of the Vendian - Riphean boundary is rather conjectural, and is usually given as 680700 Ma. However, dolerite dykes in NW Tasmania intrude the Burnie Formation with Vendian acritarchs and are K-Ar dated at 725 ± 35 Ma (Richards, in Solomon & Griffiths, 1974) or 710 Ma (McDougall & Leggo, 1965). G.Vidal quotes an unpublished Rb-Sr whole rock isochron on sediments in South Sweden containing Vendian acritarchs at 722 ± 37 Ma. An age of 725 Ma is provisionally accepted for the base of the Vendian as defined by Yakobsen & Krylov (1978). All isotopic ages are quoted in terms of the new and internationally accepted constants for RbSr and K-Ar given by Steiger & Jager (1977, 1978). International Divisions of the Cambrian, Ordovician, Silurian and Devonian and Australian stages are listed in the correlation chart (Fig. 2). In this discussion the informal terms, early, middle, and late are used to indicate only a general time division; the formal terms Early, Middle and Late are used as indicated on the correlation chart. Note that there is no international agreement on the scope of the sub-period divisions of the Ordovician; those used here follow general usage in Victoria and New Zealand (Thomas, 1960; Webby et al., 1981).

4 Sequence known to continue Transgressive base

Conglomerate with dominantly quartz clasts Conglomerate, other (mainly polymict)

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Erosion surface known to be di achronous Base (not known to be transgressi ve) Frosion surface (drawn at y o u n g e s t horizon in sequence below unconf. • Section stopped at oldest known beds but sequence presumed to continue - Section stopped at y o u n g e s t known beds but sequence presumed to continue (eg.top beds faulted out) Facies transition

Limestone Dolomi te

(unconformity)

equivalents

- Age and/or nature of contact uncertain

intrusives

volcanics

Metamorphics (amphibolite facies or higher grade)

Major vertical movements, with K/Ar resetting

Granite

commonly

Folding (orogenic), generally accompanied by metamorphism and followed by uplift and erosion. Rb/Sr resetting

E E E *

® © ©

m m

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Regional metamorphism (dynamic, thermal) to greenschist or higher grade. Rb/Sr resetting Basic volcanism and associated intrusive activity Intermediate volcanism and associated intrusive activity

Ichnofoss i1s Stromatolites

Acid

volcanism

Granite and granodiorite R 515-20 K 420

Rubidium/Strontium Potassium/Argon

emplacement

date

Fig. 2 Legend for correlation chart (Fig. 3).

Ultramafic complexes, with main period of emplacement indicated

INTERNATIONAL DIVISIONS

PERIOD

AUSTRALIAN STAGES

SOUTH AUSTRALIA YORKE IMTLOFTY RA.I FLINDERS PENINSULA KANGAROO I. RANGES

W. BARRIER I RANGE

N. S. W. GNALTA ^NALLA

ANTARCTICA

TASMANIA

TMITHTONI DUNDAS Q. M A U D M T S VICTORIA L. TROUGH TROUGH

DIAL RA. [ADAMSFIELDI N O R T H - E A S T G L E N E L G S E D I M ^ ^ M R ^ S T A W E L L L B E N D I G ^ H E A T H - [MELBOURNE TROUGH B E I J L W A R A T A H L ^ ^ FOSSEYMTS AREA TASMANIA WEST | EAST SED. B E L T S B . | C O T E B E L T D A ^ R A W E I T G U I M | M T E A S T O N BAY B E L T BELT

N I M R O D H N O R T H E R N

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INTER NATIONAL DIVISIONS

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CASTLEMAINIAN CHEWTONIAN BENDIGONIAN . . J^NCmEJLDIANPAYNTONIAN

CASTLEMAINIAN CHEWTONIAN BENDIGONIAN

IDAMEAN MINDYALLAN BOOMERANGIAN UNDILLAN FLORAN TEM PLETONI AN ORDIAN

IDAMEAN MINDYALLAN BOOMERANGIAN UNDILLAN FLORAN TEMPLETONIAN ORDIAN

TOMMOTIAN EDIACARAN

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LATE

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. ,

LATE

m n r MIDDLE

EARLY

UPPER PROTEROZOIC

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725

RIPHEAN

COMPLEX

Fig. 3 Correlation chart of representative stratigraphic columns from South Australia, Western New South Wales, Antarctica, Tasmania, Victoria and New Zealand, showing sedimentary, tectonic, igneous and metamorphic events in the late Proterozoic - Devonian geological history of the SW Pacific sector of Gondwanaland.

VENDIAN

RIPHEAN

BASEMENT

UPPER PROTEROZOIC COMPLEX

Acknowledgments

1.2 Aim and organisation The main aims of this paper are: a. To indicate the nature and timing of the main events in the sedimentary, igneous, metamorphic and tectonic history of each of the regions under study. b. To provide a reasonably detailed and precise correlation of the late Proterozoic to midPalaeozoic sequences of each region, and thus a time-stratigraphic framework within which detailed comparisons and contrasts between regions can be made. The main features and geological history of each region are briefly summarised as a background to the stratigraphic columns presented in the chart. To save space many items in the text and on the chart requiring detailed discussion or explanation are grouped together for each region in an appendix and referred to by numbered reference^26)1.3 Authorship responsibility Regional authorship responsibility is as follows: South Australia, J.B.Jago and B.Daily; Western New South Wales, B.D.Webby; Antarctica, M.G.Laird and G.W.Grindley; Tasmania, K.D.Corbett, A.V.Brown, G.R.Green, and J.B.Jago; Victoria, A.H.M.VandenBerg and H.E.Wilkinson; New Zealand, R.A.Cooper and G.W.Grindley. G.Vidal is responsible for the acritarch data. G.W.Grindley, R.A.Cooper, B.Daily and K.D.Corbett wrote the summary tectonic history (Section 9), and G.W.Grindley and R.A.Cooper are responsible for the Introduction (Section 1) and the Conclusions (Section 10).

1.4 Acknowledgements Many Australian and New Zealand geologists have joined in the Project field excursions and contributed to seminars and discussions. We are grateful to them all but particularly wish to thank O.P.Singleton, M.J.Garratt, K.A.W.Crook, E.Scheibner, M.R.Banks, E.Williams, C.A.Boulter and A.C.Coleman. For guidance in the field we thank the above mentioned and Messrs I.Duddey, P.F.Bolger, P.W.Baillie, A.C.Edwards, and Drs C.Burrett, G.Neef, and R.Williams. For assistance with field excursions, we thank W.D.M.Hall, T.Scott, S.P.Carey, P.S.Roberts, B.G.Forbes, G.W.Krieg and A.J.Wright, and for assistance in organising meetings we thank D.A.Feary and K.S.W.Campbell. Considerable assistance with field transport was received from the New Zealand Geological Survey; Department of Mines, Tasmania; Department of Minerals and Energy, Victoria; Department of Mines, South Australia; Department of Mines, New South Wales; South Australian Institute of Technology: Department of Geology, University of Adelaide; Department of Geology, University of Tasmania; Department of Geology, University of New South Wales, Broken Hill; and Electrolytic Zinc Co., Tasmania. For assistance with typing and copy editing we thank Mrs F. Tonks, New Zealand Geological Survey, and Dr N. Hawcroft, Science Information Division, Department of Scientific and Industrial Research, Wellington. The figures were draughted by Mrs M. Haronga. We wish to thank our employing organisations for supporting our participation in the Project. The Project was made possible by the funds received through the International Geological Correlation Programme. This paper is published with the permission of the Department of Mines, Tasmania, the Department of Minerals and Energy, Victoria, and the New Zealand Geological Survey.

South Australia

2. REGIONAL SEQUENCES - SOUTH AUSTRALIA Late Precambrian to Lower Palaeozoic rocks outcrop widely in the Mt Lofty Ranges, Fleurieu Peninsula, Kangaroo Island, and on Yorke Peninsula, where they are known mainly from the subsurface (Fig. 4). 2.1 Yorke Peninsula A thin platform cover of gently folded Cambrian strata rests nonconformably on Precambrian crystalline rocks of the Gawler Block on Yorke Peninsula (Fig. 4). Basal conglomerate, sandstone and arkose, sometimes glauconitic (Winulta Formation), is overlain by pale to dark limestones and interbedded dolomites (Kulpara Formation) and dark grey silty limestones and intertonguing pale archaeocyathid limestone (Parara Limestone). The Winulta, Kulpara and Parara Formations contain Early Cambrian fossils (Daily, 1976b; Opik, 1975). An uneven erosion surface at the top of the Parara Limestone is widespread with seismic records indicating that it extends east from Yorke Pensinsula, and south to the southern part of Gulf St Vincent (Stuart & Von Sanden, 1972). Resting on the erosion surface is a thin polymict conglomerate (Minlaton Formation), with carbonate, sandstone, quartzite, and gneiss pebbles, followed by a sequence of interbedded carbonate and red-green clastic formations. In the Minlaton stratigraphic bore a sequence of silts tones, shales, limestone and gypsum indicate evaporatic depositional conditions. The Ramsay, Stansbury and Coobowie Limestones contain fossils, including Redlichia of early Middle Cambrian (Ordian) age. The top red bed unit on Yorke Peninsula (Yuruga Formation), has an eroded top and is overlain unconformably by Permian and younger sediments. 2.2 Mount Lofty Ranges, Fleurieu Peninsula and Dudley Peninsula (Kangaroo Island) Throughout this region Cambrian sediments disconformably overlie late Precambrian sediments. They comprise two main depositional cycles, the Normanville Group and the overlying Kanmantoo Group (Daily et al., 1976, 1979). The Normanville G r o u p s is best exposed in the Sellick Hill area. The oldest unit, the Mt Terrible Formation, consists of a thin transgressive arkose at the base with abundant trace fossils; a phosphatic shale unit with the oldest shelly fossils known in Australians); and a cavernous weathered calcareous sandstone at the top. Shelly fossils recovered from the middle member include hyolithids, the gastropod Bemella, spicules of Chancelloria, a conodont (possibly Oneotodus) and several problematica including Heraultipegma and cf. Sachites. The occurrence of the tubular non-shelly fossil Saarina and other sabelliditids in the middle and upper member of the formation (Daily, 1976b) suggests that these intervals should be correlated with the Lantova Horizon of the Baltic Stage, Russian Platform, below which shelly fossils are unknown. Conformably overlying are two upward shallowing cycles of carbonate-rich rocks (Wangkonda Formation). The overlying limestone-shale succession (Sellick Hill Formation, Fork Tree Limestone) is separated from the Wangkonda Formation by a disconformity, marked by cut and fill structures in which hyolithids, Chancelloria and Tannuella accumulated (Daily, 1963, 1969). Tannuella is restricted to the Atdabanian of the USSR and occurs commonly in Atdabanian aged rocks in the Flinders Ranges. Calcareous algae and archaeocyathids are locally abundant, indicating a shallow water depositional environment and an early Early Cambrian age. Calcareous and phosphatic shale (Heatherdale Shale) conformably overlies the Fork Tree Limestone and represents the youngest beds of the Normanville Group. In the Truro area northeast of Adelaide, the mainly andesitic Truro Volcanics are interbedded with Normanville Group sediments.

South Australia Mt Painter

Lake Frome Embayment STUART;:::;^

SHELF ;;;;; =

GAWLER EYRE

PENINSULA

BLOCK

Cape Car not

Permian Mesozoic Cainozoic Late Cambrian Ordovician

Adelaid

^77^/^SellicksHill Kangaroo Is FJeurieu Permian & KANMANTQO post-Permian Peninsula Sediments

Murray Bridge ^

Delamerian granites and volcanics Kanmantoo Group

Cambrian Late Proterozoic (Adelaidean) Middle Proterozoic Archaean toMiddle .

Hawker Group, Billy Creek Formation Wirrealpa Limestone, Lake Frome Group and equivalents Adelaidean sediments with minor volcanics Gawler Range Volcanics Pre-Adelaidean granites, gneisses .schists and metasediments

Fig. 4 Generalised geological map of South Australia showing location of main features mentioned in text.

South Australia

At Carrickalinga Head, the basal member of the Kanmantoo Group,, the Carrickalinga Head Formation, conformably overlies the Heatherdale Shale. This represents the start of a new cycle of sedimentation and was triggered off by the Kangarooian Movements (Daily & Forbes 1969). The Kanmantoo Group as described by Daily & Milnes (1971, 1972a, 1972b, 1973) consists of a very thick conformable sequence of metasandstones, metasiltstones and phyllites. There are eight formations, viz: Carrickalinga Head Formation (base), Backstairs Passage Formation, Talisker Calc-siltstone, Tappanappa Formation, Tunkalilla Formation, Balquhidder Formation, Petrel Cove Formation and the Middleton Sandstone (eroded top). Thin conglomerate units are known from the Tappanappa and Balquhidder Formations. These conglomerate units become thicker and coarser towards the west (Daily et al., 1979). Daily & Milnes (op. cit) and Daily et al., (1979, Table 2 and p.22) considered that much of the Kanmantoo Group was rapidly deposited in a relatively shallow offshore marine environment by strong currents that 'flowed in an easterly direction sub-parallel to the southern margin of the Gawler Block which formed the contemporary shoreline of the Adelaide Geosyncline in this region'. However, other workers (e.g. Thomson, 1969; Flint, 1978; von der Borch, 1980) have suggested that much of the Kanmantoo Group was deposited as proximal to distal turbidites or in a deep sea fan environment. The Middleton Sandstone is well laminated, shows low angle cross-bedding and is of shallow marine origin. The top of the Middleton Formation is not exposed. However, it is intruded by the Late Cambrian - Early Ordovician Encounter Bay Granites and hence a substantial sedimentary cover must have existed above the Middleton Sandstone at the time of granite emplacement. These cover rocks may have included Middle and Upper Cambrian sediments and possibly even Upper Ordovician sediments (Daily & Milnes, 1973). Apart from the inarticulate brachiopod Lingulella and a few Redlichia fragments in the Carrickalinga Head Formation, the only known fossils from the Kanmantoo Group are worm burrows and a few trails.

2.3 Northeast coast of Kangaroo Island Fossiliferous Lower Cambrian strata younger than the Normanville Group outcrop on the northeast coast of Kangaroo Island (Sprigg et al., 1954; Daily, 1956; Daily et al., 1979, 1980). They form part of a thick (2700 m minimum thickness) relatively unmetamorphosed (greenschist facies) sequence of very rapidly deposited alluvial to shallow marine conglomerates and predominantly shallow marine, tidally dominated sandstones, silts tones, and shales laid down in response to the very widespread, episodic, Kangarooian Movements. The older portion of the sequence can be traced westwards into the metamorphosed Kanmantoo Group in the vicinity of King George Beach. The presence of the Carrickalinga Head Formation at the base indicates that the sequence is equivalent to the major part of the Kanmantoo Group described by Daily & Milnes (1971,1973). The following units, in upward sequence, are mapped: Carrickalinga Head Formation (base not exposed), Stokes Bay Sandstone, Smith Bay Shale, White Point Conglomerate, Emu Bay Shale and Boxing Bay Formation (top not exposed). The Carrickalinga Head Formation and Smith Bay Shale both contain trace fossils, including trilobite tracks, and fragments of Redlichia. No fossils have been found in the Stokes Bay Sandstone, but the lithologically similar Boxing Bay Formation contains trilobite tracks and various types of burrows and trails. The White Point Conglomerate consists of about 550 m of polymictic conglomerate and breccia and interbedded red and green sandstone, silts tone and shale. Desiccation cracks are common in the shales. Clasts within the conglomerates are up to 1.5 m in length; some limestone clasts contain archaeocyathids and other Early Cambrian fossils. Analysis of clast types and

South Australia

palaeocurrent data reveals that the conglomerates in both the White Point Conglomerate and Boxing Bay Formation were derived from uplifted fault blocks that lay adjacent to the present northern coastline of Kangaroo Island. Alluvial fan complexes, derived from these uplifted blocks comprised of Cambrian sediments underlain by Precambrian crystalline rocks, spread southwards onto and across tidal flats that formed the contemporary east-west shoreline. Some of the interbedded shales within the White Point Conglomerate are richly fossiliferous and contain well preserved late Early Cambrian trilobites (Balcoracania, Emuella, Estaingia, Redlichia) and Hyolithes (Daily, 1956, Pocock, 1970, Daily et al., 1979). The overlying Emu Bay Shale contains trilobites (Estaingia, Emuella, Redlichia), Hyolithes, inarticulate brachiopods, phyllocarid crustaceans (Isoxys, Tuzoia) and annelids (Sprigg et al., 1954, Sprigg, 1955; Daily, 1956; Pocock, 1964, 1970; Glaessner, 1979), indicating a late Early Cambrian age. Palaeocurrent analysis of the sequence has shown that the bulk of the sediments, other than the conglomerate facies, was spread by strong tidal currents flowing parallel to the east-west shoreline. Transport of sands within the Carrickalinga Head Formation and the Stokes Bay Sandstone was essentially towards the east and southeast, but in younger formations bipolar eastwest transport is indicated with the predominant mode to the east except for the Boxing Bay Formation where it is to the west (Daily et al., 1979, 1980). Contorted bedding, due to dewatering of rapidly deposited sands, is a conspicuous feature of many sandstones and resulted from seismic shocks accompanying the Kangarooian Movements. 2.4 Flinders Ranges The Precambrian geology of the Flinders Ranges (Fig. 4) has recently been summarized by Forbes & Coats (1976), Von der Borch (1980) and Rutland et al., (1981), from which papers the following information is derived. The oldest sediments of the Flinders Ranges, the Callanna Beds^ ), overlie the crystalline basement( ) unconformably and transgressively. The Callanna Beds consist mainly of sandstone (commonly with salt casts), siltstone, stromatolitic and evaporitic carbonates and mafic volcanics. The unconformably overlying Burr a Group rocks have a basal conglomerate and sandstone possibly deposited on tidal flats (mud cracks and salt casts) or in a shallow marine to fluviatile environment. This is overlain by stromatolitic dolomite, laminated and oolitic dolomite, siltstone and sandstone, essentially of shallow marine to paralic and even lacustrine origin (Uppill, 1980). The clastics were derived from westerly and northerly source areas. The unconformably overlying Umberatana G r o u p s ) comprises the glacigene and interglacial deposits of the Adelaidean. The lower, Sturtian glaciation left glacial and associated clastics up to 5000 m thick, but the majority are usually only a few hundred metres thick. The upper, Marinoan glacial sequence varies from a true tillite to a coarse sandstone. The interglacial period is represented by a very widespread and thick sequence of laminated siltstone and carbonate deposited in a moderately deep water marine environment and shallowing upwards into intertidal to supratidal carbonates (Preiss, 1973; Sumartojo, 1975; Daily et al., 1979). The conformably overlying Wilpena Group( ^ comprises a basal dolomite overlain by a sequence of shale, quartzite, siltstone, dolomite, limestone and sandstone, largely of shallow water marine origin. The top unit of the Wilpena Group, the Pound Quartzite contains the famous Ediacara fossil assemblage, which is confined to a thin widespread unit in the upper part of the Pound Quartzite (Glaessner & Wade, 1966; Wade, 1970; Jenkins, 1975). Cambrian rocks of the Flinders Ranges disconformably overlie the Precambrian sediments, and have been summarized by Daily (1976b). In some areas, the dominantly green siltstones of the Uratanna Formation fill basins and channels cut into the Pound Quartzite, sometimes to levels below that of the Ediacara fauna. It contains distinctive Early Cambrian trace fossils, 03

BGn

South Australia

especially Didymaulichnus, Phycodes pedum and ?Curvolithus davidis which are of Tommotian age (Daily, 1976b). The Parachilna Formation, the basal member of the Hawker Group, disconformably overlies the Uratanna Formation, or where the Uratanna Formation is absent, it rests disconformably on the Precambrian sediments. The Parachilna Formation contains trace and shelly fossils which Daily (1976a, 1976b) considers to be of Tommotian age. The Parachila Formation comprises sandstone, siltstone and shale with Diplocraterion, Plagiogmus, and other trace fossils indicative of a very shallow marine origin. A prolonged phase of mainly carbonate sedimentation followed deposition of the Parachilna Formation, and in places, the carbonate rests directly on the Precambrian rocks. Both light and dark coloured carbonates are present. According to Daily (1976b), the lighter coloured carbonates were deposited on relatively stable shelves, in conditions ranging from supratidal and intertidal to normal shallow marine environments, with the former containing few fossils and the latter containing abundant fossils including archaeocyathids, trilobites, gastropods, hyolithids and brachiopods. Darker coloured limestones forming the bulk of the Cambrian carbonates are largely but not always indicative of deeper water deposition. These carbonates sometimes contain numerous fossils but generally they are sparsely fossiliferous. Lateral and vertical facies changes within the carbonate sequence may be quite rapid (Haslett, 1975). In some areas there are considerable sequences of sandstones and shales in the upper part of the Hawker Group. Low in the carbonate sequence at least one widespread break occurs within the Ajax Limestone. The late Early Cambrian, essentially regressive, Billy Creek Formation overlies the Hawker Group with either conformity or disconformity. It consists dominantly of shallow water red to brown micaceous shale and siltstone, with minor feldspathic sandstone, dolomite and limestone. Thin tuff bands, which thicken eastwards, may have been derived from western New South Wales. Daily (1976b) considers that the Billy Creek Formation was deposited under paralic conditions. Moore (1979a, b, c) has given a detailed environmental analysis of the formation. The presence of the trilobite Balcoracania indicates a late Early Cambrian age and permits correlation of part of the Billy Creek Formation with the upper levels of the White Point Conglomerate on Kangaroo Island. Overlying the Billy Creek Formation is a carbonate-calcareous shale sequence, the Wirrealpa Limestone and equivalents (Youngs, 1977, 1978) indicating a widespread transgression. The Wirrealpa Limestone contains fossils throughout including stromatolites, archaeocyathids, gastropods, brachiopods, hyolithids, sponges and trilobites including Redlichia. Daily (1956, 1976b) considers the Wirrealpa Limestone to be of early Middle Cambrian (Ordian) age. The Wirrealpa Limestone is conformably overlain by the sediments of the Lake Frome Group, which from the base consists of the Moodlatana Formation, Balcoracana Formation, Pantapinna Sandstone and the Grindstone Range Sandstone. The source area for the Lake Frome Group appears to be the Gawler Block to the southwest. The Moodlatana Formation consists mainly of red micaceous shale, sandstone and arkose with minor carbonate horizons. Mud cracks and trace fossils are abundant. Near the top of the formation, metadoxidid trilobites are known from a thin, dark limestone unit. The Balcoracana Formation comprises cycles of red and grey-green micaceous siltstone with minor sandstone and arkose. Thin dolomitic bands, commonly stromatolitic and with diagenetic chert, alternate with the clastics. Mud cracks, halite casts and abundant trace fossils are known from the Balcoracana Formation. On the basis of one poorly preserved agnostoid trilobite cf. Lejopyge, found in the subsurface in beds assigned to the Balcoracana Formation, a late Middle Cambrian age has been suggested for the upper part of the formation (Daily & Forbes, 1969). Daily (1976b) suggested that the time of deposition of the Balcoracana Formation was one of frequent transgressions and regressions. The overlying Pantapinna Sandstone comprises mainly cross-bedded feldspathic sandstone and arkose with minor shale. Stock (1974) proposed a fluviatile origin but the occurrence of trace fossils, especially trilobite tracks and burrows (Cruziana), indicate a shallow subtidal origin. The

South Australia

Grindstone Range Sandstone is a feldspathic sandstone showing cross-bedding, slumping and mudcracks in the lower part and conglomerate and cross-bedded sandstone near the top of the exposed beds. The presence of trace fossils suggests at least some marine influence. The Pantapinna Sandstone and Grindstone Range Sandstone may be of Middle Cambrian, Late Cambrian or even of Ordovician age. No Early Palaeozoic sediments above the Lake Frome Group are known in the Flinders Ranges. Sedimentation was probably halted by the Late Cambrian - Ordovician Delamerian Orogeny (Thomson, 1969). 2.5 Tectonic history, palaeogeography The Cambrian sediments of southern South Australia were deposited around the eastern and southern margins of the Archaean to Carpentarian Gawler Block (see Daily et al., 1973 for the broad palaeogeographic framework). In some places (e.g. Yorke Peninsula) there is a thin platform cover of Cambrian sediments resting directly on the crystalline rocks of the Gawler Block. However, throughout most of southern South Australia there is an unconformity between late Precambrian and Cambrian sediments. The movements leading to this unconformity were called the Duttonian Folding by Thomson (1969). The very Early Cambrian marine transgression is represented by the basal arksoses of the Mount Terrible and Winulta Formations on Fleurieu and Yorke Peninsulas respectively. The shallow marine sedimentation initiated by this transgression was interrupted by the onset of the Kangarooian Movements in the Early Cambrian (Daily & Milnes, 1971). The sediments of the Kanmantoo Group including possible turbidites were derived from newly emergent land masses (presumably Gawler Block crystalline basement with a Late Precambrian - Early Cambrian cover) uplifted in the present Investigator Strait and Gulf St Vincent areas, as well as from the Gawler Block. The cyclic nature of the shallow water sediments of Yorke Peninsula and the presence of recurring conglomerates in the northeast Kangaroo Island fossiliferous Cambrian and the temporally equivalent Kanmantoo Group indicate the episodic nature of the Kangarooian Movements. Some of the early Cambrian sediments previously deposited on Yorke Peninsula were uplifted, stripped and redeposited as a result of the Kangarooian Movements, as is evidenced by the large gap in the Yorke Peninsula sequence above the Parara Limestone and the presence of large blocks of archaeocyathid limestone in the White Point Conglomerate and Boxing Bay Formation, Kangaroo Island. The deposition of the possible turbidites found in some of the Kanmantoo Group units was triggered by the Kangarooian Movements. The presence of older Precambrian gneisses and other crystalline rocks as pebbles within the Kanmantoo Group plus the high feldspar content of the Kanmantoo Group metasandstones indicate that the Gawler Block crystalline basement supplied most of the Kanmantoo Group sediments. On Yorke Peninsula at least, the sporadic Kangarooian Movements continued well into the Middle Cambrian and possibly on into the Late Cambrian (Daily & Milnes, 1973). Indeed mild episodic tectonic activity may have extended through until the onset of the Late Cambrian - Early Ordovician Delamerian Orogeny. It should be noted that the Kangarooian Movements of Daily & Forbes (1969) correspond to the Cassinian Uplift and Waitpingan Subsidence of Thomson (1969, 1970) and see discussion in Daily & Milnes, 1971, p.209 for details. Late Cambrian to Early Ordovician high-level granitic bodies intrude the Cambrian sediments of Fleurieu Peninsula, eastern Mount Lofty Ranges and Kangaroo Island (e.g. Sprigg et al.,1954; White et al., 1967; Thomson, 1969; Webb, 1976; Milnes et al., 1977). Similar, but only sporadically exposed granitic rocks are found intruding metamorphosed sediments (?equivalent to Kanmantoo Group) along and near the Padthaway Ridge (a much later palaeogeographic feature) which extends from near Murray Bridge in a generally southeastward direction into

South Australia

southwestern Victoria (Rochow, 1969; Webb, 1976; Milnes et al. r 1977). Feldspar quartz porphyries, feldspar porphyries and flow banded rhyolites (Mawson & Dallwitz, 1944; Mawson & Segnit, 1945; Henstridge, 1970) are also known. Two distinct groups of basic dykes cut Kanmantoo Group sediments (Daily & Milnes, 1973) and are possibly Early Ordovician in age. The striking fold patterns of the Precambrian and Cambrian sediments of much of South Australia were caused by the Late Cambrian - Early Ordovician Delamerian Orogeny. Uplift commenced in the Late Cambrian and probably caused the cessation of Kanmantoo Group sedimentation. The Encounter Bay Granites (504 - 495 Ma^) were intruded and had crystallised prior to the main culmination of the first phase of folding (with its associated schistosity development; Daily & Milnes, 1973). Rb-Sr and K-Ar data suggest that folding and regional metamorphism up to andalusite grade occurred for a further 50 Ma (Milnes et al., 1977). The Middle Ordovician dates of the granites exposed along the Padthaway Ridge are probably due to later tectonic and metamorphic overprinting. A further weak metamorphic event in the Late Silurian or Early Devonian both in the Encounter Bay area (Milnes et al., 1977) and particularly in southeastern South Australia and southwestern Victoria (Webb, 1976) may have been contemporaneous with the Benambran and Bowning Orogenies of the Tasman Fold Belt. Uplift of the region by the Late Palaeozoic exposed the granite and surrounding Kanmantoo Group metamorphics to glacial erosion (Daily et al., 1976).

Western New South Wales

3. WESTERN NEW SOUTH WALES 3.1 Barrier Range In the Barrier Range (Fig, 5) north of Broken Hill, late Proterozoic (Adelaidean) rocks of the Poolamacca, Torrowangee and Farnell Groups (Rose, 1968; Cooper, 1975; Cooper et al., 1975, 1978; Cooper & Tuckwell, 1971) rest unconformably on metamorphics of the Willyama Complex of early Proterozoic age^ ). Above the basal blanket sandstones, orthoquartzites and conglomerates of the Poolamacca Group, the Torrowangee Group comprises deposits of two glaciations (Sturtian and Marinoan) separated by an interglacial sequence (Eurowie Sub-group) of calcareous siltstone, quartzite and carbonate. The overlying post-glacial Farnell Group (Cooper & Tuckwell, 1971) comprises 6000 m of interbedded siltstone, shale, quartzite and minor limestone and dolomite. First traces of metazoan activity occur in the Fowlers Gap Formation, and a much more diverse and abundant trace fossil fauna in the still higher Lintiss Vale Formation (Webby, 1970). This latter unit is unconformably overlain by the unfossiliferous Acacia Downs Beds of uncertain age. The trace fossil assemblages of the Farnell Group are tentatively regarded as having a middle-late Vendian age (Webby, 1973)( ). 1

3.2 Bancannia Trough A structural depression referred to as the Bancannia Trough (Freeman, 1966; Brunker, Offenberg & Rose, 1967; Rose & Brunker, 1969; Wopfner, 1970, 1972; Evans 1977; Fig. 5) separates the pre-Phanerozoic basement complex of the Broken Hill Block from its counterpart, the Wonominta Block^, to the east. It is predominantly filled with Middle - Upper Devonian molasse-type 'non-marine' clastics, and is considered to have played an insignificant role in the early Palaeozoic depositional history of the region. A cross section of the structure by G.H. Packham (prepared for Planet Oil N.L. and published in Cooper, 1975, fig. 7) shows it to have a basinal configuration; others by Evans (1977) show the trough to have a graben-like shape. 3.3 Mount Wright Volcanic Belt East of the Bancannia Trough, the oldest beds exposed are the 'spilitic intermediate and mafic volcanics, chert, fossiliferous limestone and shale, named by Rose (1968) the Mount Wright Volcanics, and assigned an Early Cambrian age. The first archaeocyathids occur in thin limestone lenses near the top of the formation. Opik (1975, p.9) has recorded Chancelloria and Tommotia from a similar (or the same) horizon. Kruse (1978) has noted that in the Early-Middle Cambrian the Gnalta Shelf occupied much of the area of the Wonominta Block, and acted as the shelf margin between the ocean to the east and the emergent Broken Hill (an offshore island) to the west. Scheibner (1972) viewed the Mount Wright Volcanics as a product of island arc volcanism on the western margin of the Gnalta Shelf and, in contrast to Kruse, assumed the existence of a contemporaneously active Bancannia Trough between it and the Broken Hill Block, though he later (1976, fig. 8) reproduced Packham's Planet Oil cross sections of the Bancannia Trough which show no indication of Early - Middle Cambrian deposits preserved in the basin. Succeeding the Mount Wright Volcanics is a 1500 m thick succession of cherts, acidintermediate tuffs, siltstones, sandstones and limestones, with fossiliferous horizons containing

Fig. 5

Western N e w South Wales

Generalised geological map of the Proterozoic - Devonian rocks of northwestern New South Wales. Compiled from unpublished mapping by B.D. Webby and 1:250 000 geological sheets.

Western New South Wales

archaeocyathids, trilobites, hyoliths and ?gastropods (Cymbric Vale Formation). Opik (1967; 1975) has described the shelly faunas, and Kruse (1978), some aspects of the archaeocyathids. Both Opik and Kruse have independently made similar correlations of the Cymbric Vale fauna with levels in the late Early Cambrian (Olenellian of Opik). The 115 m thick Coonigan Formation overlies the Cymbric Vale Formation with apparent conformity in the Gnalta area. It consists of a lower limestone unit and an upper shale and siltstone unit. Some elements of the diverse, well preserved Middle Cambrian fauna have been described by Opik (1967; 1970; 1979); Shergold (1969); Jell (1975); Jell & Jell (1976); Runnegar & Jell (1976). The fauna of the limestone is referred by Opik (1967) to the Ordian, and that of the overlying shales to the Templetonian. To the east, in the Copper Mine Range (Fig. 5), a markedly different succession of deposits is represented. A flysch-like sequence named by Pogson & Scheibner (1971) the Copper Mine Range Beds are likely to be of Middle Cambrian, or late Precambrian age , unconformably overlain by the Late Cambrian - Tremadoc Kandie Tank Limestone. This is succeeded by the Cootawundy Beds (derived from the Wertago-Cootawundy Series of Kenny, 1930), a 3660 m thick succession of Lower Devonian sandstones, siltstones and conglomerates (Wilson, 1967; Rose 1974). There are still considerable doubts about the age and stratigraphical relationships of the underlying basement rocks in the isolated Mount Arrowsmith inlier to the northwest. The large core-like area of the inlier includes mafic to intermediate volcanics, and varied metasediments which have been referred to the 'Precambrian' by Wopfner (1967). However, in contrast, the volcanics are viewed by Scheibner (1972) as equivalent to the Lower Cambrian Mount Wright Volcanics. (4)

3.4 Gnalta Shelf The latest Cambrian - Early Ordovician succession of thre Gnalta Shelf (Fig. 5) is dominated by clastics derived from the south and west in successive influxes of a major delta (Webby, 1978). Chief expression of the Delamerian Orogeny is given by the major break (Mootwingee Unconformity) at the base of the latest Cambrian - Ordovician sequence, and the nature of the succeeding coarse conglomerate deposits (Webby, 1978). In the Scopes Range a 1200 m thick conglomerate succession is followed by an equally thick, alternating sequence of shallow marine to non-marine deposits, predominantly of quartz-rich sandstone type. In the Bynguano Range, to the north, a more complete record of the regressional- transgressional phases of deposition in the delta are depicted. Three stratigraphically distinct 'non-marine' conglomeratic phases are represented within the 2300 m thick latest Cambrian - Early Ordovician succession with two intervening shallow marine sandy-silty phases (Webby, 1978). Farther to the north of Mount Arrowsmith, away from the direct influence of the delta, a thinner (less than 500 m thick), finer grained, limey and more markedly marine sequence formed (Wopfner, 1967). Although no Middle - Upper Ordovician or Silurian rocks are known to be preserved on the Gnalta Shelf, the Early Devonian is represented by the Cootawundy Beds of the Copper Mine Range area (Rose, 1974). The succession unconformably underlies the Late Devonian - Early Carboniferous Mulga Downs Group and contains plant fragments and trilobite tracks. Wilson (1967) referred to sill-like 'porphyries' in the Cootawundy Beds, and Rose (1974) has noted that, whereas most of the bodies are undoubtedly dykes or sills, some of the units may be extrusive in origin. The association of Early Devonian clastics with rhyolites and quartz porphyries may support a correlation with the Rocklands Rhyolite and Grampians Group of western Victoria (H. Wopfner, pers. comm., 1977), now interpreted as having an early Devonian or older age (Spencer-Jones, in Douglas & Fergusson, 1976, p.74).

Western New South Wales

3.5 Relation to Central-Western and Eastern New South Wales In assessing relationships, it should first be noted that, whereas the most complete part of the stratigraphic record in western New South Wales ranges from late Proterozoic to early Ordovician age, the same time interval is the least well represented part of the record in the geosynclinal tracts of the Lachlan and New England Fold Belts to the east. At the surface across most of the Lachlan Fold Belt, the oldest and most widely distributed rocks are of Middle - Late Ordovician age (Webby et al., 1981). Secondly, the late Proterozoic to early Ordovician succession in its continuation to the east is largely obscured by Devonian - early Carboniferous sediments of the large, intracratonic basin (Cobar Basin), and a late Mesozoic Cainozoic cover, and consequently, the nature of the west-to-east transition from late Proterozoic? to early Palaeozoic continental shelf to ocean is unknown. In the Lachlan Fold Belt of central-western N.S. W., the basement remnants of unfossiliferous, low-grade metamorphics, including quartz-rich sandstones, schists and phyllites (Girilambone Beds and correlatives) are of uncertain, possibly Cambrian or earliest Ordovician, age. The largest remnant crops out between Cobar and Nyngan. Farther east there is only the Early Ordovician intermediate-basic volcanic complexes of the Parkes Platform and Molong High (Webby et al., 1981). Early Ordovician deposits also occur in the southern extension of the Wagga Trough in northeastern Victoria (Kilpatrick & Fleming, 1980). The Wagga Trough which has been interpreted as a marginal sea, may have existed between the Gnalta Shelf (or continental margin) and the Parkes-Molong volcanic arc through most of Ordovician time (Packham, 1973; Webby, 1976). Whether the Girilambone Beds represent Early Cambrian 'trench-fill' or 'subduction complex' deposits to the east of the Mt Wright Volcanic Belt or 'Arc' (Scheibner, 1972; 1976), or have closer links with the later-forming Wagga Trough, remains to be determined. Little is known about the relationships or significance of the tiny outcrops of late Middle Cambrian and Ordovician strata adjacent to the Peel Fault near Tamworth, in the New England Fold Belt of eastern New South Wales (Philip, 1966; Packham, 1969; Hall, 1975; Cawood, 1976; Webby et al., 1981). While the record of Middle - Late Ordovician and Silurian deposition in the Lachlan Fold Belt is reasonably complete, and the history of events can be adequately reconstructed, the lack of evidence of contemporaneous deposits in western New South Wales does little to help explain, for example, to what extent the Gnalta Shelf may have been affected by the latest Ordovician early Silurian Benambran Orogeny. The rocks of the adjacent Wagga Trough were uplifted, folded and regionally metamorphosed, and it seems likely that a significant part of the substrate beneath the large, intracratonic fault-bounded Devonian - Early Carboniferous Cobar Basin (Darling Basin of Evans, 1977) also became stabilised at this time. Early Devonian sequences of the Cobar Basin include predominantly non-marine fades with subordinate marine to marginal marine occurrences (Cootawundy Beds) in the west, and mainly marine (Amphitheatre Group) in the east (Webby, 1972). A seaway probably linked the basin with the Devonian ocean to the east, and possibly another connection existed with the Melbourne Trough to the south. Following a period of mild regional uplift and local erosion in the Middle Devonian (Tabberabberan Orogeny), the depositional history became entirely non-marine (Late Devonian - Early Carboniferous Mulga Downs Group). By latest Devonian - early Carboniferous time, the entire Lachlan Fold Belt had become stabilised and uplifted, and the margin of the Australian craton had become established along the western edge of the New England Fold Belt (Leitch, 1974; Roberts & Engel, 1980).

17 Antarctica 4. ANTARCTICA Late Proterozoic - early Palaeozoic sedimentary rocks are present throughout the Transantarctic Mountains, where they have been deposited in one of a series of linked geosynclinal troughs along the downwarped margin of the East Antarctic craton (Grindley & Warren, 1964). In West Antarctica, unfossiliferous quartz-turbidites in the Ford Ranges of Marie Byrd Land and a thick varied sequence of terrigenous sediments, quartzites and carbonates in the Ellsworth Mountains also include deposits of this age as well as younger rocks. In the Ross Sea or Pacific sector of the Transantarctic Mountains, the region relevant to the present study, the best exposed and most studied sections are in the central Transantarctic Mountains and in Northern Victoria Land (Fig. 6).

4.1 Central Transantarctic Mountains and southern Victoria Land: Beardmore Group 4.1.1 Beardmore Group This includes two late Proterozoic units, the Goldie (Gunn & Walcott, 1962) and Cobham (Laird et al., 1971) Formations. The former name is given to quartzofeldspathic metagreywacke argillite, turbidite and slate of a low greenschist facies which outcrops extensively in the coastal ranges from the Nimrod Glacier south to the Shackleton Glacier. The total thickness is unknown because of the lack of marker beds in a complexly folded terrane, but amounts to at least 6 km, without an exposed top. In the central Nimrod Glacier (Fig. 6), the Goldie Formation conformably overlies the Cobham Formation which consists of pelitic schist and hornfels with marble and quartzite layers at least 500 m thick without an exposed base. An older Precambrian terrane of higher metamorphic grade to the west (Nimrod Group of Grindley, 1963; 1972) probably provided a basement for Beardmore Group sedimentation. 4.1.2 Byrd and Skelton Groups The Byrd Group contains the thickest sequence of fossiliferous Cambrian sediments so far known in Antarctica (>8 km), is divided into four formations and rests with marked angular unconformity on the late Precambrian Beardmore Group (Grindley & Laird 1969; Laird et al., 1971). The Shackleton Limestone (Laird 1963, 1964), the lowermost formation, is also the most widespread and distinctive unit. Between the Nimrod and Byrd glaciers, the formation is over 5 km thick and is overlain unconformably by the late Palaeozoic Beacon Supergroup. The Shackleton Limestone consists dominantly of pure limestone with local lenses of clastic sediments including conglomerate and mass-flow breccias up to 150 m thick. South of the Nimrod Glacier the basal deposits are quartzites, up to 500 m thick. Near the glacier, limestone rests directly on Precambrian rocks but 50 km to the north, up to 1200 m of breccia derived from local Precambrian rocks underlies a great thickness of limestone. Most of the limestone is massive or poorly bedded with several layers showing penecontemporaneous slump folding. Sedimentary structures, including symmetrical ripple marks, large-scale cross-bedding and oolites, indicate shallow water deposition for much of the formation. South of the Byrd Glacier, desiccation structures in shales indicate supratidal conditions and a tropical climate (Burgess & Lammerink, 1979) consistent with an equatorial latitude as predicted by palaeomagnetic studies. Archaeocyathids are the predominant biota, occurring sporadically throughout the Shackleton Limestone. South of the Byrd glacier, associated fossils include trilobites, a stenothecoid mollusc and inarticulate brachiopods of Early to Mid-Cambrian affinities (C.J. Burgess, D. McKinnon, and R.A. Cooper pers. comm.). North of the Nimrod Glacier, archaeocyathids from low in

Antarctica

Fig. 6

Generalised geological map of the Proterozoic - Devonian rocks of the Transantarctic Mountains (Pacific section), East Antarctica. Compiled from Geological Maps of Antarctica, 1:1 000 000, Folio 12, Antarctic Map Folio Series. American Geographical Society, New York, 1969, locally amended by more modern mapping.

Antarctica

the formation have been positively dated as late Early Cambrian (lower Lena Stage)) by Hill (1964)(S1). Gradationally overlying and interfingering with the Shackleton Limestone south of the Byrd Glacier is the Dick Formation (Skinner, 1964, 1965), an olive-brown siliceous argillite up to 150 m thick. Overlying this with possible slight unconformity is the Douglas Conglomerate (Skinner, 1964; Burgess & Lammerink, 1979), a polymict conglomerate containing a variety of clasts including boulders of limestone closely similar to lithologies in the Shackleton Limestone, some of them containing archaeocyathids. North of the Nimrod Glacier, where the unit directly overlies the Shackleton Limestone, it is at least 1200 m, and perhaps up to 2850 m thick (Laird, 1981). East of the main outcrop of the Byrd Group are scattered outcrops of clastic sediments referred to the Starshot Formation (Laird, 1963, 1964). Near the mouth of the Starshot Glacier the formation consists of 3000 m of coarse conglomerate, mudstone, calcareous sandstone, and several thin rhyolite and trachyte flows. Although no fossils have been collected, the presence of common boulders of limestone indistinguishable from the Shackleton Limestone in the conglomerate horizons suggests that the Starshot Formation is either of similar age or younger than the Shackleton Limestone. No upper or lower contacts are known. In the McMurdo Sound region (Fig. 6), the Skelton Group (Gunn & Warren, 1962) contains carbonate (Anthill Limestone) and greywacke (Teall Greywacke) units that have not yet yielded fossils but are presumed to be Cambrian correlatives of slightly higher metamorphic grade. Younger Cambrian (?) clastics (Cocks Formation of Skinner 1982), overlie the Anthill Limestone unconformably; conglomerates with clasts of andesite, porphyrite, granite and marble suggest correlation with the Starshot Formation and Douglas Conglomerate of the Byrd Group.

4.2 Northern Victoria

Land

All known early Palaeozoic deposits of Northern Victoria Land, approximately 1000 km north of the Nimrod Glacier, are included within the Bowers Supergroup (Laird et al., 1976; 1982) the total age range of which is Cambrian to Early Ordovician. The sediments are preserved within a largely fault-bounded strip, 20-25 km wide extending southeast from the mouth of the Rennick Glacier for a distance of at least 350 km to the Ross Sea. They are in fault contact on the east with the late Precambrian (?) Robertson Bay Group - a thick folded sequence of quartzose sandstone, hornfels, phyllite and slate of geosynclinal proportions (Harrington et al., 1967; Sturm & Carryer, 1970), containing Vendian to Cambrian acritarchs and metazoan trace fossils in places. To the west, the Bowers Super Group is partly faulted and partly conformable against the older Precambrian Wilson Group (Sturm & Carryer, 1970; Dow and Neall, 1972) from which an Rb-Sr model age of 785 Ma has been obtained (Faure & Gair, 1970).

4.2.1 Wilson

Group

The basement blocks west of the Bowers Mountains and Rennick Glacier comprise biotitegarnet-plagioclase paragneiss and migmatite, biotite metaquartzite, amphibolite and rare marble, all metamorphosed to the amphibolite facies and much intruded by granitic veins and dykes. The Rennick Schists to the south (Gair, 1967) provide a link with high grade biotite-paragneiss, migmatite, graphitic mica schist and marble at Terra Nova Bay (Skinner & Ricker, 1968). Three episodes of deformation in the Lanterman Range (Bradshaw et al., 1982) indicate that the Wilson Group there is likely to pre-date the Robertson Bay Group, affected by only two deformational episodes.

Antarctica

4.2.2 Berg Group and Priestley Formation West of the Bowers Mountains, metagreywacke and phyllite of slightly higher metamorphic grade but of similar lithofacies to the Robertson Bay Group form the basement of the Morozumi Range (Sturm & Carryer, 1970; Dow & Neall, 1974). About 250 km west of the Rennick Glacier mouth, similiar metagreywacke, phyllite, and rare marble form the Lev Berg Mountains (Klimov & Solov'ev, 1960; Solov'ev, 1960) and from which Riphean acritarchs have been reported (Iltchenko, 1972). Further to the south, the Priestley Formation of the Terra Nova Bay area (Ricker, 1964; Skinner & Ricker, 1968) comprises a more variable sequence of spotted slates, phyllites, quartzites and minor limestones, that may correlate with the Berg Group 500 km along strike to the northwest. The age relationships of the various metagreywacke terranes cannot be determined directly. 4.2.3 Robertson Bay Group The Robertson Bay Group (Fig. 6) occupying the Admiralty and Victory Mountains and the coastal region between Robertson Bay and the Rennick Glacier forms a thick sequence (6 km + ) of quartzofeldspathic metagreywacke and cleaved argillite in regular alternating beds up to 6 m thick. Graded bedding, cross-bedding and flute and load casts are locally abundant, indicating turbidity current deposition. Finer-grained beds are well-cleaved grey-green slates and phyllites, from which numerous K-Ar whole rock ages between 450 and 500 Ma have been obtained (Adams et al., 1982). On the Pennell Coast east of the lower Rennick Glacier, Riphean acritarchs have been obtained from phyllites and slates of the Anare and northern Bowers Mountains (D.S.Solov'ev, pers. comm., 1972), but the stratigraphic relations with the Robertson Bay Group further east and south are unknown. Some horizons have common metazoan trace fossils suggesting a latest Precambrian or younger age (Wright, 1980). In the Tucker Glacier Robertson Bay area (Harrington et al., 1967), dark grey, simply folded semischist, phyllite and slate are contact-metamorphosed to hornblende-hornfels grade by plutons of the Upper Devonian Tucker Granodiorite. A southern provenance is indicated by palaeocurrents (Wright, 1980). 4.2.4 Bowers Supergroup Three major units are recognised: the Sledgers Group, the Mariner Group, and the Leap Year Group, the latter two units separated by an unconformity. The Sledgers Group, which rests conformably on the Wilson Group, is at least 3500 m thick. It is composed in its northwestern portion mainly of angular unsorted basaltic breccia with some thin flow units and interbedded units of shallow water muds tone, sandstone, conglomerate, and limestone (Glascow Volcanics). The volcanics thin to the south and are absent in some localities, and interfinger with deeper-water mudstone and well-sorted volcanogenic fine sandstone (Molar Formation). Interspersed in these fine-grained sediments are lenticular mass movement deposits. Although previously taken as of Vendian to Early Cambrian (Cooper et al. 1982) age the Sledgers Group is now understood to be largely of Middle Cambrian age (R.A. Cooper, J.B. Jago, A.J. Rowell pers. comm.). The Mariner Group conformably overlies Sledgers Group. At least 2000 m thick, the Mariner Group, represents a transgressive/regressive sequence dominated by shallow and marginal marine environments. In the north the basal few metres consist of brown muddy sandstone and mudstone showing desiccation cracks and arthropod trails, overlain by approximately 100 m of quartzitic sandstone, and several hundred metres of calcareous mudstone with fossiliferous limestone lenses. Further south this trangressive sequence is absent and fossiliferous calcareous

Antarctica

mudstone directly overlies volcanic conglomerate. The regressive portion of the sequence is wellexposed at the head of Mariner Glacier where, in a 1600 m continuous sequence, fossiliferous calcareous mudstone passes upwards into wavy-bedded fine sandstone, hyolithid limestone, and finally red-brown coloured, cross- or wavy-bedded sandstone with mudcracks, relatively prolific trace fossils, and rare shelly fossils. The group shallows upwards into intertidal deposits (Andrews & Laird, 1976). Shelly fossils (mainly brachiopods and trilobites) are relatively common throughout and give an age ranging from late Middle Cambrian (Lejopyge laevigata Zone) to middle or late Late Cambrian (Cooper et al., 1976, 1982). A regional unconformity, resulting from uplift and erosion of perhaps 2 km or more of Mariner Group sediments in the north of the area (Bradshaw et al., 1982; Laird et al., 1982), separates the Mariner Group from the overlying Leap Year Group, exposed in two separate strips on the eastern and western margins of the Bowers Mountains. In the eastern strip, at least 3 km and perhaps up to 7 km of mainly fluvial, commonly cross-bedded, quartzose sandstone and minor quartzose conglomerate (Camp Ridge Quartzite) is exposed. No shelly fossils are known, but trace fossils have been collected from horizons near the base of the unit, and may indicate local marine influence (Laird et al., 1974; Cooper et al., 1976). In the western strip, the Leap Year Group is represented by two fluvial formations. The older, polymictic Carryer Conglomerate reaches a maximum thickness of 800 m in the lower Carryer Glacier, but thins southward to disappear near the head of Sledgers Glacier. The overlying Reilly Conglomerate consists of quartzose conglomerate and minor quartzose sandstone at least 300 m thick, and may be a stratigraphic equivalent of the Camp Ridge Quartzite (Laird et al., 1982). Age diagnostic fossils are absent but a late Late Cambrian to Ordovician age is considered probable. Palaeocurrent data and facies relationships within the Bowers Supergroup suggest the Sledgers and Leap Year Groups and perhaps also the Mariner Group were deposited in an elongate northwest-southeast trending basin - the Bowers Trough (Laird et al., 1982) - which acted as a depocentre for sediments from Middle Cambrian to possibly Ordovician time. 4.3 Tectonic history and palaeogeography 4.3.1 Central Transantarctic Mountains Cambrian sedimentation along the present trend of the Transantarctic Mountains from the Byrd Glacier to the Weddell Sea began on the site of an earlier geosyncline in which a great thickness of sediment, mainly sandstone and mudstone, had accumulated. These flyschoid sediments - Beardmore Group of Late Precambrian age, had been folded and the geosyncline everted during the late Precambrian Beardmore Orogeny (Grindley & McDougall, 1969) and subsequently eroded. Cambrian sedimentation in the Nimrod Glacier area was dominated by shallow water carbonates. Facies relationships suggest biohermal development on a technically unstable shelf with a shoreline to the west. Tectonic uplift of the western margin of the basin during the Middle Cambrian may be indicated by the great thickness of locally derived conglomerate forming the Douglas Conglomerate. Sedimentation further offshore may be represented by the possibly partly contemporaneous clastics of the Starshot Formation and correlatives lying to the east of the limestone belt. The sedimentary record is incomplete in the Nimrod Glacier area, and the sequence of events subsequent to early Middle Cambrian times uncertain. However, uplift, deformation, and metamorphism of both Precambrian and Cambrian sediments attributed to a major widespread tectonic event, the Late Cambrian Ross Orogeny, occurred between about 500-530 Ma (Adams, Gabites & Grindley, 1982). This was followed in the Ordovician (450-500 Ma) by the widespread intrusion of granites belonging to the Granite Harbour Intrusive Complex (McDougall & Grindley, 1965). Younger ages (380-440 Ma) for some Starshot Formation slates are thought to be related to continued uplift of the orogenic belt until perhaps the Early Devonian.

Antarctica

4.3.2 Northern Victoria Land The tectonic history of northern Victoria Land during the same period differs in some essentials from that of the Nimrod Glacier area. Marine transgression on folded Precambrian rocks accompanied by basaltic volcanism occurred during Early to Middle Cambrian times in a graben or grabens formed during a period of block faulting. Shallowing of the basin occurred in late Middle Cambrian times in a period of tectonic calm, which lasted until mid Late Cambrian times. Regression of the seas in the mid or late Late Cambrian heralded new uplift culminating in gentle tilting and erosion of the sediments of the Bowers Trough. A concentration of K-Ar metamorphic dates between 450 and 475 Ma from older Bowers Supergroup sediments (Adams et al., 1982) indicates the close of a period of metamorphism possibly associated with the Ross Orogeny or with intrusion at depth of parts of the Granite Harbour Intrusives (giving K-Ar ages of 450-500 Ma) which outcrop west of the Bowers Trough (Sturm & Carryer, 1970, Gair et al., 1969). There is no evidence for accompanying folding, but the reactivation of the Bowers Trough by block faulting in the Late Cambrian or Early Ordovician and its infill with coarse clastic deposits is an expression of important tectonic activity at this time. K-Ar dates of 466-483 Ma on Wilson Group (Adams et al., 1982) probably date uplift. Tectonic activity culminated in the Late Silurian to Early Devonian (dated at 380-420 Ma, Adams et al., 1982) Borchgrevink Orogeny, which resulted in folding of the Bowers Supergroup. This was followed by the injection of granites (Admiralty Intrusives) and eruption of minor rhyolites (Gallipoli Rhyolites) in the Late Devonian to Early Carboniferous (360-385 Ma) (Gair et al., 1969; Nathan, 1971; Dow & Neall, 1972). The tectonic, igneous, and sedimentary histories of the Nimrod Glacier area and northern Victoria Land during latest Precambrian to early Palaeozoic times are so different that the sediments are likely to have accumulated in subparallel but completely independent basins (Laird & Bradshaw, 1982).

Tasmania

5. TASMANIA An almost complete sequence of Lower to Middle Palaeozoic rocks, ranging from Cambrian to Middle Devonian in age, occurs in western Tasmania between extensive areas of Proterozoic basement rocks. The eastern part of the State, by contrast, is occupied by an Ordovician to Devonian flysch sequence (Mathinna Beds) on unknown basement. Cambrian troughs in the western area have a complex filling of flysch sediments with major acid and basic volcanic accumulations and disrupted ultra-mafic complexes. Final filling of the troughs was by siliceous conglomerate and sandstone in the Late Cambrian - Early Ordovician, after which the troughs were overlapped by Ordovician platform limestone and Silurian to Lower Devonian shallowmarine clastics. Folding in the Middle Devonian Tabberabberan Orogeny affected virtually all the lower Palaeozoic rocks, inluding the Mathinna Beds, but the fact that tectonic transport directions are opposed across the Tamar Contact Zone suggests that the Mathinna Beds may have been brought into juxtaposition after the folding. Discordant granite-adamellite plutons of Late Devonian - Early Carboniferous age intrude the folded rocks in both western and eastern Tasmania (Fig. 7).

5.1 Precambrian basement rocks Tasmanian Precambrian rocks are predominantly of sedimentary origin, and include regionally metamorphosed greenschist facies assemblages and relatively unmetamorphosed assemblages. The met amorphic rocks constitute the large Tyennan Nucleus in the central part of the area, and the smaller Forth Nucleus on the north coast (Fig. 7). For simplicity, these terms are used throughout, although the structural significance of the units may have varied with time. Maximum metamorphic grade is upper greenschist facies, the rocks being derived mainly from inter-bedded siltstone-orthoquartzite sequences with minor carbonate. Minor amphibolite and eclogite derived from basic-intermediate igneous rocks also occur. The several phases of folding with an early main period of metamorphism define the Frenchman Orogeny (Spry, 1962; Williams, 1978). Rb-Sr dating suggests an age of 800 Ma for the main metamorphic event (R&heim & Compston, 1977). The largest area of comparatively unmetamorphosed rocks is the Rocky Cape Region, in the northwestern part of the State (Fig. 7). A narrow belt of greenschist facies regional metamorphics, with amphibolite dykes (the Arthur Lineament), transects the region, and is transitional with adjacent unmetamorphosed rocks along its western margin at Wynyard (Gee, 1977). A variety of sequences has been described west of the Lineament. Along the Pieman River, in the south, is a sequence of slate, quartzite, conglomerate, mafic volcanics and dolomite (Spry, 1964). In the Arthur River area the metamorphics pass westward into a quartzite-pelite sequence, followed by a siltstone-sandstone sequence (NcNeill, 1961). On the north coast, the Rocky Cape Group (550 m + ) is a thick shallow-marine sequence of orthoquartzite and siltstone with minor dolomite and subgreywacke. Bimodal current directions in the quartzite suggest a palaeoslope to the northwest, but the source area for the sand was granitic or gneissic, not the Tyennan metasediments (Gee, 1971). Siliceous, carbonaceous meta-siltstone comparable with the Rocky Cape Group forms the basement (at about 1500 m) in the Esso Clam I drill hole, some 40 km west of the coast (Fig. 7). On the western side of King Island a sequence of strongly deformed quartzite, slate, phyllite and schist is intruded by syntectonic granites which give Rb-Sr ages on muscovite of about 735 Ma and K/Ar dates up to 725 Ma (McDougall & Leggo, 1965). No Precambrian granites are known on mainland Tasmania. Basement rocks on the eastern part of King Island (below the Cottons Breccia of Jago, 1974) are unmetamorphosed and less deformed calcareous siltstone and fine sandstone.

Tasmania

WAGGA

STAWELL BELP< MELBOURNE

TROUGH

Easton

Provincej ROSEDALE

WRENCH

ZONE

ROSEDAU^MUOHi GIPPSLAND.

BASIN

[TORQUAY EMBAYMENT

OTWAY

Wilsons Promontory

BASIN

FLINDERS ISLAND VO-D KINGI ISLAND

SMITHTON TROUGH

Gry0f*Pl

Beaconsfieli

CAPE REGION

750/Bischoj \ > 4 o n a h ) f f RoseberyU

Dg^S^I I ^ L \

"Zeehank

O'Connors — Peak-

\V€ cLQueenstown

ADAMSFIELD 'JUBILEE BLOCK

HOBARl

Mount Read Volcanics belt

Fig. 7

Simplified geological map of Victoria, Bass Strait and Tasmania, showing major early Palaeozoi features and Cainozoic structures. Fine dashed lines are aeromagnetic anomalies. Compiled from 1:2 500 000 Geological Map of Australia (B.M.R., 1976), Abele et al., 1976; Beattie, 1978; Browi 1976; Robinson, 1974; Blake, W.J.R. (unpubl. M.Sc. thesis), by K.D. Corbett. P C , Precambrian;^ Cambrian; O, Ordovician; S, Silurian; D, Devonian; C, Carboniferous; u, Upper; m, Middle; 1,lowei g, granite; v, volcanic. Ultramafic rocks in black. Other symbols as in Fig. 2 and Appendix.

Tasmania

To the east of the Arthur Lineament on the north coast is a complexly folded thick sequence (5000 m +) of interbedded quartzwacke turbidites and slaty mudstone - the Burnie Formation of Gee (1977). Spilitic pillow lavas occur in a few areas, and dykes and sills of sodic dolerite (Cooee Dolerites) are common. Some of the sills show slurried tops suggestive of intrusion into still-wet sediments (Crook, 1979), but others appear to be syn-tectonic. Deformation and metamorphism of the Burnie Formation and the Rocky Cape Region generally is attributed to the Penguin Orogeny, and K-Ar dates on the Cooee Dolerites are thought to date the early phase of this Orogeny. Dates of 725 ± 35 Ma (revised from Richards, in Spry, 1962) and 710 Ma (McDougall & Leggo, 1965) have been obtained, suggesting correlation with the King Island deformation. KAr dates of 670-690 Ma obtained from slates in the Burnie and Oonah Formations (Black & Adams, 1980) confirm a late Proterozoic age for the Penguin Orogeny. Rocks similar to the Burnie Formation, although with less obvious turbidite characteristics, occur east of the Arthur Lineament in the Zeehan area, where they comprise the Oonah Formation (Blisset, 1962). Carbonate horizons and altered mafic volcanics of possible alkaline type occur in the upper part of the Oonah Formation (Blisset, 1962; Foden, 1973). Two large inliers of Oonah-type rocks occur within the Dundas Trough at Dundas and Mount Bischoff. An unmetamorphosed quartzwacke sequence similar to the Burnie Formation constitutes the Badger Head Region near Beaconsfield (Gee & Legge, 1974). In the Adamsfield area, unmetamorphosed sequences of dolomite, mudstone, quartzite and quartzwacke occur within the poorly-known Jubilee Block (Corbett, 1970). Dolomite of presumed Precambrian age rests unconformably on the Tyennan Nucleus rocks in several areas in the vicinity of the Jane River (Spry, 1962). 5.2 Smithton Trough and King Island The Smithton Trough lies within the Rocky Cape Region. The base of the trough sequence is the Smithton Dolomite, comprising some 600 m of dolomite and laminated black and grey chert, with rare stromatolitic horizons. At the base is a thin quartzite and siliceous conglomerate unit which rests unconformably on, and regionally transgresses, the Rocky Cape Group. A diamictite containing abundant dolomite clasts overlies the dolomite in the Arthur River (Griffin & Preiss, 1976). Some of the clasts contain a stromatolite similar to Baicalia burra, a type typical of the Skillogalee Dolomite of the Adelaidean Burra Group in South Australia but not recorded from the Smithton Dolomite. Other clasts appear to have been soft at the time of deposition. Although a debris-flow mechanism for the diamictite is favoured, a glacial origin cannot be ruled out. Overlying the diamictite, apparently conformably, is a thick sequence of tholeiitic spilite, mudstone, greywacke, tuff and volcanic breccia which extends into the Smithton area. No acid volcanics are known. At Christmas Hills this sequence contains late Middle Cambrian trilobites (Jago & Buckley, 1971; Gulline, 1959). A second trilobite locality recently discovered may be Late Cambrian (P.W.Baillie, pers. comm.). No top is known to the sequence, and there are no known Ordovician or younger Palaeozoic rocks in the Smithton area. On the east coast of King Island a diamictite containing blocks of dolomite, quartzite and metasiltstone conformably overlies a calcareous siltstone - fine sandstone sequence (Jago, 1974). The diamictite (50-100 m) is conformably overlain by siltstone and dolomite (60 m) with intercalated tholeiitic pillow lavas and massive basalts (now spilites), followed by a sequence of picritic hyaloclastites, basalt flows and pillowy flows (Waldron, 1977; Solomon, 1969). The age of the sequence is not known, but correlation with the Smithton sequence seems likely, although deposition may have occurred in a separate basin.

Tasmania

5.3 Dundas Trough The Dundas Trough is an irregular meridional structure, about 40 km wide, lying between the Tyennan Nucleus and the Rocky Cape Region. It appears to branch westwards in the Zeehan area, and joins with the east-west oriented Fossey Mountains Trough to the north. Apart from the Precambrian inliers at Dundas and Mount Bischoff, there are two large Precambrian blocks (which appear to be of metamorphosed Tyennan type - Baillie et al., 1978) in the Cape Sorell area, suggesting that the trough is really part of a complex system of interconnected troughs developed around basement blocks. A continuous belt (except for younger cover) of acid to intermediate volcanics, the Mount Read Volcanics, occupies the eastern part of the trough, and interfingers westwards with Cambrian greywacke-mudstone sequences containing basic volcanics and ultramafic-mafic complexes. 5.3.1 Early trough sequences The oldest trough sequence, the Success Creek Group (Taylor, 1954) comprises about 1000 m of fine-grained siliceous sandstone, mudstone and minor dolomite, and overlies the Oonah Formation in the Pieman River with landscape unconformity (Brown, 1980a, b). Above the contact is a sedimentary mixtite, containing angular to rounded clasts of the underlying quartzite, carbonate and sandstone. The unconformity represents a structural hiatus as earlier suggested by Williams et al., (1976). Dolomite-chert lenses, some of which have been mineralised, occur in the upper part of the sequence at Renison Bell, where acritarchs of Vendian aspect have been recovered. Solomon (1965) and Williams (1978) have suggested correlation of the Success Creek Group with the Smithton Dolomite. Conformably overlying the Success Creek Group is an unfossiliferous turbidite sequence of volcaniclastic lithic wacke, silts tone and mudstone called the Crimson Creek Formation (Taylor, 1954; Blissett, 1962; Brown, 1980a, b). This extensive sequence contains abundant chert and spilitic pillow lavas (tholeiites) in the Cleveland area, near Mount Bischoff (Collins, 1981), and the greywackes are generally rich in basaltic detritus. However, acid volcanic detritus also occurs (Brown, 1980b, c), suggesting contemporaneity with the early Mount Read Volcanics. 5.3.2 Ultramafic - mafic complexes Partially-serpentinized ultramafic - mafic bodies have been tectonically emplaced into the Crimson Creek Formation and its correlates in many parts of the trough (Brown et al., 1980). Several of these bodies lie along the boundary between the Crimson Creek Formation and the overlying fossiliferous Dundas Group and correlates. Basal conglomerates of the latter contain ultramafic detritus in at least three localities. The largest body is the Heazlewood River Complex, west of Mount Bischoff (Rubenach, 1973), which has a basal dunite followed by a sequence of interlayered olivine pyroxenite and orthopyroxenite, the upper part of which is feldspathic. A second association of dominantly harzburgite with interlayered orthopyroxenite and peridotite, and their plagiocloase-bearing equivalents, occurs to the east of the lower zone. Subaqueous volcanic rocks are associated with the intrusives, and the complex has been described as an ophiolite (Rubenach, 1973; Williams, 1978). However, the dolerites and volcanic rocks are quartz and olivine tholeiites with Ca-poor pyroxene, and are chemically and mineralogically unlike those from oceanic environments or those associated with the Oman and Troodos ophiolite bodies (Creenaune, 1980). Rather than being formed at an oceanic spreading ridge, the evidence suggests that the Heazlewood River Complex could be a crustal cumulate body which was dismembered during continental rifting, tectonically emplaced into overlying sedimentary rocks and then intruded by quartz tholeiite volcanics (Brown et al., 1980; Creenaune, 1980).

Tasmania

The Serpentine Hill Complex, northeast of Zeehan, consists of layered pyroxenite and harzburgite grading upwards into a transition group of pyroxenite, norite and bronzite gabbro that in turn grades into hypersthene gabbro and microgabbro (Rubenach, 1974). These rocks are spatially associated with subaqueous lavas of quartz tholeiite composition similar to those at Heazlewood River. 5.3.3 Fossiliferous sequences (Dundas Group and correlatives) Overlying the Serpentine Hill Complex is a fossiliferous flysch sequence, about 3000 m thick, of interbedded mudstone, greywacke, conglomerate, mafic volcanics and minor felsic volcanics known as the Dundas Group (Elliston, 1954). Detritus derived from spilite and ultramafic rocks occurs in the base of this group (Rubenach, 1974). Recent mapping (by A.V.Brown) indicates that the basal formations (Red Lead Conglomerate, Hodge Slate, Razorback Conglomerate, lower part of Brewery Junction Formation) are faulted against the upper formations (upper Brewery Junction Formation, Fernfields Conglomerate, Comet Slate, Fernflow Formation, Climie Formation, Misery Conglomerate) and that graded greywacke beds are more abundant in the upper sequence, the lower sequence possibly being partly shallow water in origin (Brown, 1980c). The oldest fossils in the type section are agnostids and dendroids of Middle Cambrian (P. atavus - P. punctuosus Z o n e ) age in the Hodge Slate, but a slightly older fauna (P. gibbus Zone) occurs in a silstone block probably from below the Red Lead Conglomerate. A unit of siltstone and sandstone occurs below the Red Lead correlate in several areas, and mafic volcanics are intercalated with the conglomerate in the Ring River east of Serpentine Hill. Fossil horizons occur from the upper Brewery Junction (late Middle Cambrian and early Late Cambrian) up to the Climie Formation (middle Late Cambrian Jago, 1978, 1979a). The conglomerate units within the sequence are notably lenticular. Chert clasts to cobble size predominate in the Red Lead and Razorback Conglomerates, while boulders of Precambrianderived quartzite become prominent in some members of the Fernfields and Fernflow Formations. The Misery Conglomerate (150 m) conformably overlies the green and purple greywacke and mudstone of the Climie formation, and consists of red to purple, pebble to boulder grade conglomerate with clasts of quartzite, chert, jasper and quartz. Correlatives of the Dundas Group, with fossiliferous horizons, occur in various parts of the trough (Corbett & Brown, 1976), and there are also a number of lithologically similar sequences in which fossils have not been found. The sequences are generally conglomeratic, and indicate considerable tectonic instability within the trough, with much erosion of earlier trough units. Some of the sequences, e.g. in the Professor Range area south of Zeehan, contain abundant Precambrian-derived quartzwacke sandstones (Baillie et al., 1978). A n unusual sequence containing siliceous sandstone, the 'Rosebery Group' (Taylor, 1954), is faulted against the Mount Read Volcanics at Rosebery. It comprises black slate and volcaniclastic sandstone, followed by Precambrian-derived quartzwacke and slate (Stitt Quartzite), dolomitic siltstone and shale, polymict conglomerate, and an horizon of acid tuff similar to that which overlies the Rosebery ore horizon in the Mount Read Volcanics. Recent work (Green et al., 1981) suggests that the sequence consists of several fault blocks and may be faulted against the Crimson Creek Formation to the west. The lithologies most resemble those in the Dundas Group, but the age and stratigraphic significance of the 'Rosebery Group' remain uncertain. 5.3.4 Mount Read

Volcanics

The Mount Read Volcanics consist dominantly of rhyolitic to dacitic tuffs, breccias, lavas and intrusives, with locally-abundant andesitic rocks, minor basalts, and lenses of black shale and siltstone. The belt is about 15 km wide, and overlaps the western and northern margins of the

Tasmania

Tyennan Nucleus. Subdivision into a central belt dominated by lavas, ash-flows and intrusives, and a flanking western belt of interbedded pyroclastics and sedimentary rocks, (chiefly lithic wackes and shales), is possible in most areas (Corbett, 1979, 1981; Collins et al., 1981). The western sequence grades into sedimentary sequences of Dundas Group type in some areas. The eastern margin of the belt rests unconformably on the Tyennan Nucleus in many places, with a basal siliceous conglomerate. The volcanics have been affected by regional lower greenschist facies metamorphism and local intense hydrothermal alteration. Massive and disseminated volcanogenic Cu-Pb-Zn sulphide deposits occur in a number of places (e.g. Mount Lyell, Hercules, Rosebery, Que River). Small granite-adamellite bodies, usually somewhat altered and deformed, occur in a number of places along the belt and appear to be at least partly of sub-volcanic origin. Blocks of the Darwin Granite, near Queens town, occur in an unconformably-overlying sequence of volcanics and sediments which in turn is unconformably overlain by the Late Cambrian - Early Ordovician Owen Conglomerate (Corbett, 1979). The Murchison River Granite has given a minimum K-Ar date on hornblende of 520 ± 15 Ma (McDougall & Leggo, 1965), and a U-Pb zircon age of 511 Ma has been obtained on the Darwin Granite (Black & Adams, 1980). A maximum possible age of 540 Ma, based on zircon data, has been suggested for a central belt lava at Queenstown (ibid.). Minimum ages from several small bodies at the northern margin of the Tyennan Nucleus (Dove River Granite) range from 460-510 Ma (McDougall & Leggo, 1965). A limestone containing late Middle Cambrian fossils occurs within the volcanic sequence at Queenstown, and was deposited after a local hiatus in volcanism during which most of the mineralization at Mt Lyell occurred (Jago et al., 1972; Corbett et al., 1974; Corbett, 1981). The sequence above the limestone, the Tyndall Group, comprises a lower unit of crystal tuff, agglomerate, laharic breccia and shale (Comstock Tuff), and an upper unit of volcaniclastic conglomerate and sandstone. A black shale within the volcanic sequence at Que River, north of Rosebery, also contains late Middle Cambrian fossils (Gee et al., 1970). Although acritarchs have been recovered from shale units in some parts of the sequence, their significance is still being assessed. 5.3.5 Owen Conglomerate and correlatives The Owen Conglomerate comprises up to 1200 m of siliceous shallow-marine to non-marine pebble to boulder conglomerate and cross-bedded sandstone derived from the Tyennan Nucleus. This sequence blanketed much of the earlier Mount Read Volcanic belt, and was largely deposited in a series of grabens fringing the nucleus. Control of deposition by contemporaneous movement on the Great Lyell Fault is clearly evident at Queenstown (Corbett et al., 1974). A proximal turbidite sequence with graded sandstones, conglomerates and slump sheets (Newton Creek Sandstone Member) occurs at the base of the formation at the Tyndall Range 20 km north of Queenstown, and contains a middle Late Cambrian marine fauna (Corbett, 1975a). This part of the sequence is probably equivalent to the upper part of the Dundas Group. The relationship of the Owen Conglomerate to the Tyndall Group varies from unconformity in places (e.g. Gooseneck, South Darwin Peak) to apparent conformity in others (Tyndall Range, Mount Lyell). In many places, the conglomerate rests directly and unconformably on the main volcanic sequence (e.g. Mount Jukes), and the term 'Jukesian Movement' relates to these areas (Carey & Banks, 1954). It seems preferable to retain this term for the break at the base of the Owen Formation rather than apply it to the base of the Tyndall Group (cf. Corbett et al., 1974). In the Queenstown area the uppermost part of the Owen Formation consists of some 10 m of fine conglomerate and sandstone of Early Ordovician age known as the Pioneer Beds. This unit rests unconformably on the upturned beds of the underlying part of the formation (Haulage

Tasmania

Unconformity) and transgresses the Great Lyell Fault to rest directly on volcanics (Corbett et al., 1974). It is overlain by Ordovician limestone. An equivalent sandstone unit, usually somewhat thicker, transgresses most of the Dundas Trough sequences and overlaps onto the Precambrian areas. 5.4 Dial Range Trough This narrow northerly extension of the Dundas Trough lies between Burnie Formation to the west and metamorphosed Tyennan-type rocks of the Forth Nucleus to the east. Thrust blocks of Burnie Formation occur on the eastern flank of the trough. Spilites (olivine tholeiites) are extensively developed within the trough, and are closely associated with bodies of laminated chert up to 1000 m thick correlated with the Barrington Chert. Burns (1964) places the chert and spilite between two fossiliferous late Middle Cambrian sequences, but this may be a tectonic succession resulting from overthrusting. The fossiliferous sequences (Cateena and Radfords Creek Groups) comprise mudstone, greywacke, minor acid volcanics, and conglomerates with chert and spilite detritus, and range in age from middle Middle Cambrian (P. atavus Zone) to late Middle Cambrian (P. nathorsti Zone) and from late Middle Cambrian (L. laevigata II or III Zone) to early Late Cambrian (late Mindyallan) respectively (Jago, 1973, 1976a, b, 1979a). Megabreccias and chaos structures containing large blocks of limestone, dolomite, chert, spilite, quartzite, conglomerate and sandstone, occur on the foreshore between Penguin and Ulverstone, and appear to be younger than or equivalent to the Radfords Creek Group. A massive body of porphyritic andesite-dacite (Lobster Creek Volcanics) in the central part of the trough may be a late-stage intrusion. A dyke of similar composition at Gunns Plains gives an Early Ordovician age (480 ± 18 Ma) by the Rb-Sr method (Jago et al., 1977). Unconformably overlying the Cambrian sequence is a chert-clast conglomerate up to 540 m thick (Duncan Conglomerate) followed by siliceous sandstone of probably Early Ordovician age and Gordon Limestone correlate. The conglomerate overlaps Burnie Formation rocks to the west at Sulphur Creek. 5.5 Fossey Mountains Trough and Beaconsfield The complex sequence of greywacke, mudstone, chert, conglomerate, and acid to basic volcanic rocks in the Fossey Mountains Trough is poorly known, and there is virtually no fossil control. The extensive Barrington Chert interfingers with the earlier clastic sequences in places, and is overlain by a sequence with chert-rich conglomerates (Jennings, 1963, 1979). Acid volcanics become predominant in the southern part of the trough, in continuity with the Mount Read Volcanics, and three small granitic plutons at the boundary with the Tyennan Nucleus are probably of Cambrian age (McDougall & Leggo, 1965). Mafic to intermediate volcanics occur at Beulah and in an isolated window to the south-east at O'Connors Peak (Matthews, 1974), but no ultramafic rocks are known. The siliceous Roland Conglomerate rests unconformably on the Cambrian rocks, and is overlain by the Lower Ordovician Moina Sandstone followed by a well developed Gordon Limestone sequence. At Beaconsfield, on the eastern margin of the Badger Head Block, an ultramafic-gabbro body and a disrupted sequence of greywacke, mudstone and chert occupy a series of east-dipping fault slices (Gee & Legge, 1974). The only volcanic rock known is a small altered andesite body. Trilobites of late Middle Cambrian age occur in one unit. The ultramafic body contains serpentinized cumulate orthopyroxenite with minor peridotite, and the layered mafic rocks consist mostly of two-pyroxene gabbro. Interlayered pyroxenites occur within the gabbroic zone. Hornblende gabbro intrudes the layered sequence, but no other intrusive or extrusive rocks

Tasmania

are known to be associated with this body. The Cambrian rocks are overlain by siliceous conglomerate and sandstone of the Cabbage Tree Formation, which consists largely of troughderived chert detritus and contains detrital chromite at the base. The Gordon Limestone correlative overlies this.

5.6 Adamsfield

Trough

This trough lies at the apparent eastern margin of the Tyennan Nucleus, and partly overlaps the 'Jubilee Block' of unmetamorphosed dolomite, mudstone, quartzite and greywacke to the east. The older rocks of the trough are arranged in complex meridional belts, probably largely of tectonic origin. Recumbently-folded diamictites (Wedge River Beds) of probable Precambrian age at the southwest margin of the trough are unconformably overlain by siliceous conglomerate and sandstone, containing unidentifiable trilobite fragments (Turner, 1979) which passes up into a well-bedded lithic-wacke turbidite sequence. The latter is in tectonic contact with a disrupted sequence of mudstone, massive greywacke and banded chert with minor basic to intermediate volcanics and mafic intrusives. A block of bedded siltstone and greywacke within this sequence on the Gordon Road contains recently-discovered trilobites of probable middle Middle Cambrian age (Turner, 1979). A similar chert-mudstonegreywacke sequence is exposed in a small area east of the main part of the trough on Mount Mueller (Corbett 1970). Acid volcanics previously reported from this sequence may represent boulders derived from overlying Carboniferous tillite (N.J.Turner, pers. comm.). In the northern part of the trough, an implied unconformity, represented by a sedimentary breccia, separates an area of foliated rock sequences to the west from a group of unfoliated sequences to the east (Brown et al., in press). The foliated rocks include a phyllite-dolomite sequence (probably Precambrian), a sequence of alternating quartzwacke and schistose siltstone, a lens of pebbly sandstone and cobble conglomerate, and a bedded chert-greywacke- mudstone sequence. The breccia contains blocks of locally derived material as well as rounded clasts of Precambrian quartzite. The unfoliated sequences include a tectonic lens of massive quartzite and associated red siltstone and sandstone at Wings Lookout (Wings Sandstone), and the disrupted mudstone-greywacke-chert sequence which extends south to the Gordon Road. Most of the lenses or fault blocks dip steeply east. The Trial Ridge Beds, of siliceous conglomerate and sandstone, with a fossiliferous siltstone of late Middle Cambrian age in the middle part, unconformably transgress the older rocks in the northern part of the trough. The lower part of this sequence is of shallow-water origin, while the middle and upper parts appear to be proximal flysch deposits (Corbett, 1970; Brown et al., in press). An alpine-type ultramafic body occupies a major fault zone for much of the length of the trough, and consists largely of serpentinite with lenses of interlayered low-alumina orthopyroxenite and peridotite (Brown, 1971). The mineralogy and layering suggest a cumulate origin at high temperature and low pressure from a high-Mg andesitic magma (Varne & Brown, 1978). The ultramafic body was fault emplaced through the Trial Ridge Beds, and is unconformably overlain by the Denison Subgroup, which contains ultramafic detritus and middle Late Cambrian fossils at the base at Adamsfield. The Denison Subgroup (Corbett, 1975b) is equivalent to the Owen Formation of the Dundas Trough, and comprises a proximal quartzwacke flysch at the base (Singing Creek Formation, 720 m), followed by the shallow marine Great Dome Sandstone (510 m), the non-marine Reeds Conglomerate (up to 1560 m), and richly fossiliferous Early Ordovician sandstone and mudstone of the Florentine Valley Formation (450 m; Corbett & Banks, 1974; Stait & Laurie, 1980).

Tasmania 5.7 Ordovician and Siluro-Devonian

post-trough sequences

A widespread thick limestone unit conformably overlies the Lower Ordovician fossiliferous sandstone in most areas and is generally preserved in large Tabberabberan synclines. The limestone is best developed near Adamsfield, where it reaches a maximum thickness of about 2100 m and is known as the Gordon Subgroup (Corbett & Banks, 1974, 1975). Elsewhere the term Gordon Limestone is generally applied. The Ordovician biostratigraphy of Tasmania has recently been reviewed by Banks and Burrett (1980). Four formations are recognised in the Florentine Valley section near Adamsfield. The basal Karmberg Limestone (450 m) is rich in siltstone and has a chert-rich member at the top. Shelly faunas and rare phyllograptids suggest a Whiterockian (approximately Castlemainian) age. The Cashions Creek Limestone (150 m) is characterised by abundant oncolites (Girvanella sp.) and has a shelly fauna indicating a Chazyan (Yapeenian-Darriwilian) age. The Benjamin Limestone (1200 m) consists of a Lower Limestone Member (Middle Ordovician), Lords Siltstone Member, and Upper Limestone Member, the latter with corals and conodonts indicating an EastonianBolindian age. The upper formation consists of poorly-exposed siltstone and sandstone (Westfield Beds of Corbett & Banks, 1974; now incorporated in the Arndell Sandstone by Baillie, 1979), and contains graptolites and shelly faunas which span the Ordovician-Silurian boundary (Baillie, Banks & Rickards, 1978). The overlying shallow-marine clastic sequence in the Florentine area (Tiger Range Group of Baillie, 1979) has a quartz sandstone unit at the base (Gell Quartzite, 130 m), followed by the Richea Siltstone (130 m) with monograptids of Late Llandovery age, the poorly- fossiliferous Currawong Quartzite (150 m; pre-Devonian), and at the top the McLeod Creek Formation, comprising over 400 m of siltstone and fine sandstone which is probably a correlative of the Bell Shale. A fairly complete limestone sequence also occurs in the Fossey Mountains Trough, where it rests in places on the richly fossiliferous Caroline Creek member (Chewtonian) of the Moina Sandstone. At Mole Creek the base of the limestone is similar to the Cashions Creek Formation, with a late Chazyan fauna. Several shelly and conodont faunas occur above this, and near the top the richly- coralline Den Member appears to be of Eastonian age. The limestone is conformably overlain by a sandstone correlated with the lower part of the Eldon Group, and this is unconformably overlain by Permian strata. A number of fragmentary limestone sequences are known in western Tasmania, where outcrop is generally poor and sections mostly faulted. The limestone is only a few hundred metres thick in some areas, and in places contains a high proportion of shale. The oldest unit known is from the Olga river area and is probably equivalent to the Cashions Creek Formation, but most of the other reported shelly faunas are younger than this (Banks, 1962a). A well-developed Siluro-Devonian sequence, known as the Eldon Group, occurs in the Zeehan area (Banks 1962b). At the base, the poorly-fossiferous Crotty Quartzite (480 m) rests disconformably (in places) on the limestone, and is possibly of late Llandoverian age. It is followed by the Amber Slate (240 m), which contains limestone lenses in places and rare shelly fossils suggesting a late Llandoverian age. The poorly-fossiliferous Keel Quartzite (40-100 m) follows, and is overlain by the Austral Creek Siltstone (60 m), which contains shelly fossils and graptolites of lower Ludlow age. The overlying Florence Sandstone (480 m) contains rich shelly faunas indicating a Pridolian to possibly Early Devonian age, and is followed by the extensive Bell Shale (500 m + ), a sequence of mudstone and fine sandstone containing mid-Early Devonian faunas (Talent & Banks, 1967). An essentially shallow water environment, with some evidence for deepening in the upper part where there is less sandstone, has been suggested for the Bell Shale by Baillie & Williams (1975).

Tasmania

A coarse bioclastic limestone lens (25 m +) occurs within, or at the base of, the Bell Shale correlate on the lower Gordon River (Gee et al., 1969). At Point Hibbs, on the west coast, a thick coralline limestone unit (170 m) of middle to late Siegenian age (Flood, 1974) occurs within a Devonian sandstone-conglomerate sequence (Banks 1962b). In the Beaconsfield-Frankford area, Gordon Limestone occurs in a number of fault blocks and gradationally overlies sandstone of the Cabbage Tree Formation (Gee & Legge, 1974; Gulline, 1981). At least 300 m of limestone, with intercalated minor siltstone units, occurs at Beaconsfield and contains conodonts of probable early Llanvirnian age (M.R.Banks, pers. comm.). In the Flowery Gully area, about 510 m of limestone with sparse shelly fossils and conodonts of late Arenig - early Llanvirn age (Banks & Burrett, 1980) is overlain, probably disconformably (Noakes et al., 1954) by several hundred metres of interbedded slate, siltstone and quartzose sandstone. The latter sequence contains rare graptolites and some shelly fossils (brachiopods, trilobites, gastropods) of probable Late Ordovician age (Gulline, 1981; M.R.Banks, pers. comm.). Although possible correlation of the siltstone-sandstone sequence with the Mathinna Beds to the east has been suggested (Banks, 1967, 1962a), the general character of the sediments and the fauna suggests a shallow-water environment, in contrast to the notably flysch-like character of the Mathinna Beds. 5.8 Mathinna Beds of Eastern Tasmania The term Mathinna Beds is applied to all the pre-Permian folded sedimentary rocks in eastern Tasmania. The beds occur extensively in the northeast, and also on Maria Island, and are folded and cleaved and intruded by granitic rocks. Two broad associations are recognised - a siltstoneslate association with minor sandy intercalations, which occurs in two narrow belts near the western margin of the outcrop area (Fig. 7; McCleneghan & Baillie, 1974), and a sandstonemudstone association which is more extensive. The two slate belts possibly represent the same unit repeated, and appear to be older than the sandstone association (Marshall, 1969). The sandstones are quartzwackes, and typically show graded bedding and other turbidite features. Detrital components include quartz, quartzite, plagioclase, orthoclase, muscovite, sericite, chlorite, zircon, tourmaline, rutile, and carbonaceous material. Sparse current-direction data indicate currents from the west, northwest and southwest. Stratigraphic thicknesses are uncertain because of structural complications. The only fossils so far known from the siltstone-slate association are poorly preserved graptolites of Loganograptus type near Back Creek Bluff. These indicate an Early Ordovician (?Castlemainian) age (Banks & smith, 1978; Banks & Burrett, 1980). Several widely-distributed fossil localities are known from the sandstone-mudstone association. Vascular plant remains occur at six localities, and Chondrites from the north coast at Weymouth. Fragmentary transported brachiopods, corals, bivalves, cephalopods and dacryoconarids occur at Scamander, on the east coast, and indicate a Devonian (possibly Eifelian) age, and a Monograptus from north of Scamander is probably of Pragian age (Rickards & Banks, 1979). 5.9 Tectonic, metamorphic, and igneous history 5.9.1 Evolution of the Cambrian Troughs A two-stage evolution involving an early extensional phase (Early ?Vendian - Cambrian), in which tholeiitic volcanics were erupted and the ultramafic-mafic complexes were formed, and a Middle to Late Cambrian phase which involved some compression and in which earlier trough units (including the ultramafics) were technically disrupted and eroded, is indicated for most of

Tasmania

the Tasmanian Cambrian troughs (Williams, 1978). The compressional phase seems to have been most intense at Adamsfield, where a series of tectonic wedges of different ages (including Precambrian) were faulted against one another during possibly two phases of deformation prior to the late Middle Cambrian. Deformation within the Dundas Trough appears to have been relatively mild, with only minor cleavage development. There must have been considerable disruption by faulting, however, to uplift the various intra-trough units and allow their erosion into the Dundas Group and correlates. Tectonic emplacement of chert lenses in the Dial Range Trough may have occurred at this time. The age range of the Mount Read volcanism is difficult to determine, but the bulk of the volcanics in the Queenstown area appear to be Middle to Late Cambrian (Corbett, 1981, 1979). Considerable uplift of the Tyennan Nucleus occurred towards the end of the Cambrian to provide detritus for the extensive Owen Conglomerate and its correlatives, which accumulated in rapidlysubsiding fault-controlled basins fringing the nucleus. Some areas such as the Dial Range Trough and Beaconsfield received mainly trough-derived chert detritus during this period. Conditions stabilised as the fault troughs were filled with coarse material, following which shallow-marine sand deposition transgressed over the troughs and onto the Precambrian highs during Early Ordovician time. The apparent similarities between the Mount Read Volcanics and Andean-type continentalmargin volcanics has led to speculation regarding a possible subduction zone either in the Dundas Trough or east of the Tyennan Nucleus (Solomon & Griffiths, 1972, 1974; Corbett et al., 1972; Solomon, 1977; Crook, 1980). It has also been suggested that the Dundas Trough may originally have been a broad oceanic area, and that the present juxtaposition of Precambrian blocks (after closing of the ocean) is largely fortuitous (e.g. Scheibner, 1974). The available evidence, however, strongly suggests that the trough represents a rift structure developed in continental crust along a Precambrian boundary, and that the former existence of a subduction zone within the trough is unlikely (Williams, 1978). For example: (a) Inliers of Rocky Cape-type rocks occur east of the main ultramafic belt at Dundas and Mount Bischoff, and Burnie Formation rocks occur on either side of the Dial Range Trough. (b) The unconformity between Oonah Formation and Success Creek Group indicates that the trough sequences in the western part were deposited directly on Rocky Cape basement. The contact is unlikely to be a suture line between units previously separated by a broad ocean. (c) The possibility of the Burnie-Oonah Formations representing a subduction complex related to the formation of the Mt Read Volcanics (e.g. Crook, 1980a, b, 1981) is refuted by the radiometric data, which indicate that deformation of the Burnie Formation occurred nearly 100 Ma earlier than the eruption of the volcanics (Black & Adams, 1980). (d) The dismembered ultramafic-mafic complexes could be crustal cumulate bodies emplaced in a rift rather than formed at a spreading ridge. (e) The metamorphic belts and extreme deformation expected at a subduction zone appear to be lacking - mapping to date suggests the trough deposits are relatively simply deformed (Brown, 1980b, c). (f) The Mount Read Volcanics could represent crustal melts developed in a rift situation, and are possibly comparable with rhyolites in the 'failed-arm' rift of the Lebombo Monocline in Mozambique (Brown et al., 1980). The possible existence of a west-dipping subduction zone under eastern Tasmania during the Cambrian, making the Dundas Trough a marginal sea or back-arc basin, is more difficult to evaluate. The restricted occurrence of the Mount Read Volcanics against the western and northern margins of the Tyennan Nucleus is difficult to explain by this model, but might possibly be due to localisation along major rift faults. Minor basic-intermediate and possibly acid volcanic activity is indicated in the Adamsfield area, and altered schistose basic tuffs which form the pre-

Tasmania

Permian basement in a drill hole at Hobart (Everard, in Leaman, 1976) are considered to be chemically similar to high-Al basalts of the Mount Read Volcanics (Solomon & Griffiths, 1974). However, evidence in the form of feeder dykes in the Precambrian or detritus in the Early Ordovician conglomerates, is lacking to support the contention of Solomon & Griffiths that the volcanics originally extended across the Tyennan Nucleus to Hobart. The deformation within the Adamsfield Trough could perhaps be attributed to collision with a continental block coming from the east, and such a collision might also explain the apparent change to compressional conditions in the Middle and Late Cambrian in the Dundas Trough.

5.9.2 Tabberabberan Orogeny The Cambrian to Early Devonian rocks of both western and eastern Tasmania are extensively deformed by flattened parallel folds with associated cleavage. Undeformed cave deposits in folded Gordon Limestone at Eugenana, just south of the Forth Nucleus, contain spores of late Middle Devonian age (Balme, 1960), indicating that the folding in western Tasmania occurred between the middle Early Devonian (topmost Eldon Group and its correlates) and late Middle Devonian. K-Ar dates of 400-430 M A from slates in the Bell Shale and Tyndall Group at Queenstown (C.J.Adams, pers. comm.) and from the Rosebery Mine (Black & Adams, 1980) appear to record this deformation and metamorphism. In eastern Tasmania, Cocker (1977) has recorded Rb/Sr isochron dates of 400-425 Ma on the Mathinna Beds, indicating that deformation and metamorphism in this area was probably largely synchronous with that in western Tasmania, which is correlated with the Tabberabberan Orogeny. The major features of the Tabberabberan deformation have been reviewed and in part redefined by Williams (1978). In the western area, the early phase folds tend to parallel the margins of the major Precambrian blocks, and appear to be related to convergence between them. The second phase folds have a NW or NNW trend and a more pronounced cleavage, and in the Fossey Mountains - Beaconsfield area are related to thrust faults indicating transport from the NE. Folds in the Mathinna Beds have NW-trending hinge lines and SW-dipping axial surfaces, and penetrative cleavage. A large recumbent syncline, overturned from the west, has its hinge zone about 25 km east of the Tamar River, and the folding in NE Tasmania generally suggests tectonic transport from the SW. This is opposite to that on the western side of the Tamar Contact Zone.

5.9.3 Late Devonian - ?Early Carboniferous granitic intrusions Granitic bodies which truncate the Tabberabberan fold structures are widespread in Tasmania, and give radiometric dates ranging from 395 to 342 Ma (recalculated from McDougall & Leggo, 1965; Cocker, 1977). There is some suggestion that those bodies in eastern Tasmania (mostly Middle to Late Devonian) may be somewhat older than those in western Tasmania (Late Devonian to Early Carboniferous). However, Green (1978; and pers. comm.) has suggested that this may be partly an apparent effect due to a combination of long cooling histories and dating and sampling methods. The granites generally have narrow contact aureoles (0.5-2 km). Foliations defined by mineral alignments have been mapped in several of the northeastern plutons (e.g. Ringarooma Sheet, Brown et al., 1977). A dominant northwest to north-trending foliation in the two largest bodies (Blue Tier and Scottsdale batholiths) is discordant to the granite contact in several areas and is parallel to a crenulation cleavage in the Mathinna Beds between the bodies (N.J.Turner, pers. comm.). Turner (in Williams, 1978) has suggested that the granite foliations and crenulation cleavage are related to a late-stage deformation involving eastwest flattening.

Tasmania

5.9.4 Tamar Contact Zone The contrast in pre-Carboniferous geology between eastern and western Tasmania has led to speculation that the two areas were juxtaposed by a wrench fault passing along the Tamar River and continuing southwards to somewhere between Hobart and Maria Island (Williams & Threader, 1971; Williams, 1978). Various re-assemblies of Australia and Antarctica have also referred to a major shear in approximately this location (e.g. Crawford & Campbell, 1973; Harrington et al., 1973). The site of the possible fracture is buried beneath younger rocks (including the Cainozoic Tamar Graben), the closest separation being some 16 km near Beaconsfield. There is no apparent evidence of transition between the shelf deposits to the west and the flysch-like Mathinna Beds to the east, but on the other hand it is not yet certain that a compressed transitional sequence does not exist beneath the younger rocks. The composition of the Mathinna Beds does not suggest immediate or complete derivation from western Tasmania (e.g. the lack of basic volcanic detritus), and in any case the incoming sediment must have bypassed the Ordovician carbonate shelf. The opposed directions of tectonic transport in the Tabberabberan folds strongly suggests that the juxtaposition occurred after the main folding. The time interval between the folding, at 400425 Ma (dates on Mathinna Beds and Bell slates), and granite emplacement (oldest dates 395 Ma) appears to be too small to allow for major transcurrent movement before the granites were emplaced. If the granite foliations and crenulation cleavage in the Mathinna Beds are related to movement on the fracture zone, as suggested by Williams (1978), then the movement probably occurred during or soon after granite emplacement and was probably sinistral. On the other hand it is possible that the granite foliations and crenulation cleavage are not related to such movement but were impressed beforehand, possibly by a continuation of the Tabberabberan stress field with some influence by granite emplacement. In this case, any major transcurrent movement (whether sinistral or dextral) would have occurred after the granites were emplaced and foliated (youngest granite age 345 Ma) but before deposition of the Late Carboniferous tillites at about 300 Ma.

Victoria

6. VICTORIA Six major meridional belts, recognised in the 'basement' sedimentary rocks of Victoria, represent broad depositional troughs which formed and filled in a complex way from the Cambrian to the Devonian (Figs 7, 8). Older troughs generally lie in the west and younger troughs in the east but successively younger troughs were superposed in part or in whole on the rocks formed in older troughs; the boundaries of the belts rarely coincide with the known or inferred boundaries of the original trough sequences. Thus the Bendigo Trough sequence is inferred to underlie the Melbourne Trough sequence, well to the east of the present Bendigo Sedimentary Belt. The inferred relations between trough successions are shown on the schematic time-space diagram (Table 1). Basement below the oldest trough successions is not exposed and its nature unknown. Structurally complex, north-south trending narrow linear belts with cores of Cambrian sediments, metavolcanics and other igneous rocks (greenstones) separate some of the trough sequences and are referred to in Victorian literature as Cambrian axes (Mount Stavely, Heathcote, Waratah Bay and Mount Wellington Axes). With the exception of the Grampians Belt, the sedimentary successions of the Glenelg and Stawell Sedimentary Belts are poorly exposed, and little known, in marked contrast to the successions of Central and Eastern Victoria.

6.1 Glenelg Sedimentary Belt (western part) A thick, tightly folded, unfossiliferous sedimentary sequence Glenelg River Beds<Grb) crops out in the valley of the Glenelg River and its tributaries in western Victoria (Fig. 8). The predominant sediments are graded quartz greywacke and laminated slate, with subordinate lithic greywacke, black slate, argillaceous dolomitic limestone, laminated dolomitic slate, and rare volcaniclastics including the lithic greywacke. The depositional depression in which the sediments formed has been named the Glenelg Trough (Thomas et al., 1976). In the Wando Vale area near the western limit of the belt, the sediments have been affected by regional metamorphism associated with emplacement of the Wando Granodiorite (Wells, 1956) in the Late Cambrian to Early Ordovician^ 2 \ A late Proterozoic or Early Cambrian depositional age is tentatively adopted here. Dykes or sills of meta-gabbro, meta-dolerite, and amphibolite and pods of mylonitic dunite serpentinite intrude both the sediments and their metamorphic derivatives^1). They pre-date the deformation and metamorphism.

6.2 Glenelg Sedimentary Belt (eastern part) Poorly known slate and greywacke and their metamorphic derivatives associated with the eatern margin of the Wando Granodiorite in the Balmoral area probably represent the eastern extension of the Glenelg River Beds. Between these exposures and the next bedrock exposures to the east in the Black Ranges, an extensive cover of flat-lying rhyolitic lavas and pyroclastics (Rocklands Rhyolite^), Spencer-Jones, 1965) is tentatively regarded as Silurian. Sediments associated with the greenstone belts of the Black Ranges and Mount Stavely outcrop poorly and are of uncertain affinity; they are tentatively included here as part of the Glenelg Trough.

Victoria

6.2.1 Black Ranges In the Black Ranges (immediately to the west of the Grampians Trough in Fig. 8) a faultbounded inlier of now lateritised greenstone (metabasite), chert and shale with steeply plunging fold axes (Spencer-Jones, 1965) is known only from poor outcrops. An associated belt of sediments in fault contact with Black Ranges Sandstone (Grampians Group) includes black shales, and is thought to be probably younger than the greenstone. 6.2.2. Stavely Belt (based partly on unpublished work by Pennzoil of Australia Ltd) Recent mapping by G.L. Buckland shows that the core of the southern part (Mount Stavely south to the Hopkins River north of Chatsworth) of the greenstone belt known as the Mount Stavely Axis is composed of andesitic breccia and serpentinite with lesser rhyolite, andesite, dacite, basalt, chert and lapilli tuff together with intercalated volcaniclastic sediments (Mount Stavely Complex s s). The sediments occur mainly in the eastern part of the belt. The sequence dips very steeply to the east, and is presumed to young eastwards but contacts with flanking sediments (Glenthompson Beds) are faulted on both sides of the belt. In the northern part of the Axis (shown in Fig. 8 along the line of the Woorndoo Fault), a similar assemblage of volcanics and sediments outcrops as topographic highs at Mount Drummond, Mount Dryden and Jallukar Hill (Buckland, 1980). Contacts with adjacent metasediments (?St Arnaud beds) are generally obscured but apparently faulted. Regional acromagnetics indicate that the northern part of the Axis probably represents a distinct belt, rather than a continuation of the Stavely Belt that has been offset by cross-faulting (Buckland, 1981). Cherts near Mount Stavely have yielded Protospongia (Thomas et al., 1976) but no other fossils have been recorded. By analogy with the better known greenstone belts of the Heathcote and Mount Wellington Axes the age is tentatively taken as Early Cambrian. 6.2.3 Sediments associated with the southern part of the Mount Stavely Axis In the Glenthompson-Wickliffe-Chatsworth area, massive arkosic sandstone and greywacke with minor interbedded siltstone (Glenthompson beds Gt ) lie both to the east and west of the Stavely Belt and are thought to be only slightly younger than the Mount Stavely Complex. The sediments are intruded by the Wickliffe Rhyolite. Farther away from the Stavely Belt, the sediments are more typically turbiditic^Gwc\ Their relationship with the arkosic and tuffaceous rocks near the axis is uncertain but they probably follow them conformably. At Gray Ck, in the southwest, thin calcareous mudstone is interbedded with slightly metamorphosed siltstones, suggesting a transition to Glenelg River beds lithology. The metamorphism is due to the nearby Bushy Creek Granite which intrudes the sequence. At Chatsworth, in the south, turbiditic sandstones are interbedded with thin shale units. At Wickliffe, in the east, mudstones and siltstones are more prominent, and are intruded by dykes of Wickliffe Rhyolite. Metadolerite dykes similar to those intruding the Glenelg River sequence also occur. 6.2.4. Grampians Belt Between the Black Ranges Belt and the Mount Stavely Axis about 6000 m of quartzose sandstone, red siltstone and mudstone (Grampians Group0®) were deposited in a rapidly subsiding trough or graben, which may have resulted from rifting (Spencer-Jones, 1976). The eastern limit of outcrop is the Woorndoo Fault, inferred from steep tilting of Grampians Group sandstones at Woorndoo (Spencer-Jones, 1965), Lake Alexander and Lake Bolac (Wilkinson, 1978).

Victoria

GLENELG AND STAVELY BELTS, GRAMPIANS "TROUGH"

STAWELL, BENDIGO, HEATHCOTE BELTS

MELBOURNE TROUGH, MT. W E L L I N G T O N A N D W A R A T A H BAY B E L T S Howitt Trough Sediments

UPPER DEVONIAN to LOWER CARB LOWER DEVONIAN

SILURIAN & DEVONIAN

UPPER DEVONIAN

| Granitoids

7 MIDDLE DEVONIAN

I Rr Rocklands Rhyolite | Wr | Wickliffe Rhyolite

UPPER DEVONIAN

GIenthompson - Wickliffe • Chatsworth Sediments

LOWER DEVONIAN

Glenelg River Beds (high T low P mm)

Undated

| Grij| Glenelg River Beds

LOWER - MIDDLE ORDOVICIAN

| Gt | Glenthompson Beds

CAMBRIAN

Stavely Greenstone

UPPER ORDOVICIAN to LOWER CAMBRIAN

Granitoids

I +

+| Granitoids

p1™ Bendigo Trough fill

EH • [CB] | WWGGI | Walhalla Group

LOWER DEVONIAN

Darraweit

Guim

• DJ Province Sediments

/ ] Rhyodacite

+ | Granitoids

B CAMBRIAN

Undated

| Gg | Grampians Group

Granitoids LOWER ORDOVICIAN

and Volcanics; ED Cauldron Volcanics

SILURIAN - LOWER 1 MU | DEVONIAN

SILURIAN

1 Me Ri Bo

MIDDLE to

UPPER ORDOVICIAN

St Arnaud Beds

LOWER to MIDDLE ORDOVICIAN

Lower Upper Ordovician Goldie Chert Monegeetta Shale Knowsley East Fm Heathcote Greenstone

LOWER CAMBRIAN to LOWER DEVONIAN

Mount Easton Shale Riddell Grits and Unnamed Bolindian

L£J

Bell Point & Waratah Ls Digger Island Ls. Howqua Shale Garvey Gully Fm.. Dolodrook Ls. Greenstone of Waratah Bay Greenstone of Wellington River Jamieson Greenstone

E A S T E R N VICTORIA

Undated

LOWER CARBONIFEROUS

rz 1 L _ d Gra,1lt0,ds

Tv Thorkidaan Volcanics | Mm | Mitta Mitta Volcanics

LOWER SILURIAN

B g Buchan Group I W e I Wenthworth Group

LOWER _ DEVONIAN

Granitoids

„ Wombat Creek Group

^ Wc

M I D D L E I?I SILURIAN

UPPER DEVONIAN |* . * | Non - marine Sediments MIDDLE to UPPER rz i „ DEVONIAN L _ J Granitoids

Etnan0 G r ° u P

UPPER SILURIAN . | Granitoids

LOWER to UPPER ORDOVICIAN

Post - Devonian cover

-1 Granitoids

Omeo and Kuark Metamorphics

| M e ? | ? Mount Easton Shale

| Hb | Hotham Beds

Large gravity anomalies, at least in part associated with buried Cambrian Greenstone

| Sr | Snowy River Volcanics Large magnetic | _ J R J Jemba Rhyolite

LOWER ORDOVICIAN

| L P | Turbiditic Sediments

Fig. 8 Legend for geological map of Victoria (Fig. 9).

anomalies associated

with non - outcropping Greenstone

Cambrian

Fig. 9

Simplified geological map of Victoria showing distribution of major early Palaeozoic rock units, sedimentary belts and major structural features e.g. Cambrian 'greenstone axes'. Compiled from Geological Map of Victoria (1975), updated by more modern mapping, by A.H.M. VandenBerg.

Victoria

Spencer-Jones (1965) defined four formations. The oldest is the Redmans Bluff Sandstones, followed by the Silverband Formation, Mount Difficult Sandstones and Victoria Range Sandstones. The upper two units are not in contact, and some overlap may be involved. The base of the sequence is not exposed, but near Willaura, east of the Grampians, an outlier of Grampians type sandstone has a basal conglomerate resting on Wickliffe Rhyolite and including pebbles of the rhyolite. An upper limit for the Grampians Group is set by Lower-Middle Devonian ages obtained on granite bodies which intrude it. The Mafeking Granodiorite gave K-Ar hornblende ages of 375 ± 7 Ma and 394 ± 8 Ma, and the Mackenzie River Granodiorite gave K-Ar biotite ages of 403 and 400 Ma (Bowen, 1975). The dates are in conflict with the Middle Devonian to Carboniferous age previously assigned on fossil evidence by Talent & Spencer-Jones, (1963), who described Lingula borungensis, 'Physonemus' micracanthus, ostracodes, and elasmobranch dermal denticles from Unit 3 of the Silverband Formation; it is now recognized that the fossils are not particularly age diagnostic. The most likely age is Late Silurian to earliest Devonian, especially in view of the fact that the Mackenzie River Granodiorite intrudes the Mount Difficult Sandstone which overlies the Silverband Formation.

6.3 Stawell Sedimentary

Belt

The western boundary is taken as the inferred eastern boundary fault of the northern part of the Mount Stavely Axis, probably the northward continuation of the Woorndoo Fault (Wilkinson, 1978). Between this fault and the Stawell Fault is a zone of considerable structural complexity, including the Mount Ararat greenstone belt. East of the Stawell Fault there is less structural complexity. The eastern boundary is the so-called Ballarat-Wedderburn Line which separates the unfossiliferous sediments of the Stawell Sedimentary Belt from the richly fossiliferous Lower to Middle Ordovician sediments of the Bendigo Sedimentary Belt. The sediments represent the Stawell Trough of Thomas et al., (1976). Between the Stawell Fault and the Ballarat-Wedderburn Line is a thick sequence of unfossiliferous sediments, including slate, rare carbonaceous slate, siltstone and greywacke showing effects of low grade regional metamorphism and localised higher grade metamorphism associated with Lower Devonian granite intrusions. The name St Arnaud BedsSa is proposed (H.E.Wilkinson, in prep.). Volcanic rocks, volcaniclastics and limestones are unknown. Grading, frequently cyclic, fine-scale cross-bedding, and flame structures suggest a turbiditic origin. Greenstone belts are known in two areas close to the western margin of the Stawell Trough. The metamorphic complex forming Mount Ararat, about 12 km east of the Mount Stavely belt, includes actinolite schists, amphibolites and hypersthene bearing gneisses recently suggested to have been derived from tholeiitic lavas, minor intermediate lavas, pyroclastics and terrigenous sediments (Dronseika, 1974) subjected since to burial metamorphism and subsequent metamorphism associated with the adjacent Ararat granite pluton. This greenstone belt is fault bounded, and part of a structurally complex belt of metamorphosed sediments and metamorphics associated with the Ararat Granite. Diamond drilling on the Stawell Goldfield by Western Mining Corporation located a subsurface greenstone occurrence, called the Magdala Footwall Sandstone by Clappison (1965), who assigned an Early Ordovician or Late Cambrian age. Originally described as a dense rock of doubtful origin composed mainly of albite, inferred to be albitised basic volcanic rocks with similarities to some of those of the Heathcote Axis. It appears to be conformably overlain by the Mine Schist which includes discontinuous lenses of chert (Magdala Chert). The Mine Schist is in turn overlain by a slate-sandstone sequence ( = St Arnaud Beds).

Victoria

The St Arnaud Beds are therefore younger than the greenstones. The lack of graptolites has led most previous workers to regard them as earliest Ordovician or Cambrian in age. They are intruded by Lower Devonian granites, which give a minimum age of deformation and may have been folded and metamorphosed in the Early Ordovician (see note 5). There is evidence for at least two periods of deformation (multiple cleavages, re-folded bedded quartz veins, etc.). Age is taken as Cambrian. The relationship to the fossiliferous Ordovician of the Bendigo Sedimentary Belt has not yet been clarified, but preliminary mapping in the Avoca area suggests either a major structural break, or a major unconformity with the regional strike changing by at least 15°. 6.4 Bendigo Sedimentary

Belt

The belt consists of Lower to Middle Ordovician (Lancefieldian to Darriwilian) sediments and is bounded by the Ballarat-Wedderburn Line< ) to the west and the Heathcote Belt and Djerriwarrh Fault^ ) to the east. The sequence is largely of turbiditic origin (Hills & Thomas, 1954), and consists of: quartzose greywacke; siltstone; black, sometimes siliceous shale; some gritstone, and very rare very thin cone-in-cone limestone. Volcanics and volcanogenic sediments are unkown. The lower part of the sequence in the Romsey district (Romsey Group ) consists of lithic quartzose greywacke ('proximal' turbidites) and siltstone, alternating with black and grey siliceous shale and uncommon soft shale, and several bands of lithic gritstone. The group overlies Goldie Chert with apparent conformity, and contains Lancefieldian and Bendigonian (Lai to Be4) graptolites (Cooper & Stewart, 1979), phyllocarids, and rare inarticulate brachiopods. Thickness is about 1200 m, with the Bendigonian accounting for only about 200 m (VandenBerg & Wilkinson, in prep.). To the west the sequence shows a gradual upward change from predominantly sandstone (proximal turbidites) in the Lancefieldian to predominantly shale in the Darriwilian. A complete Lancefieldian (La2) to Darriwilian (Da3) graptolite sequence is preserved and provides the basis for the Early and Middle Ordovician standard zonation used throughout Australasia (Harris & Thomas, 1938b; Thomas, 1960b, Webby et al., 1981). Shelly fossils are rare, and are either benthonic or occur as comminuted fragments in turbidites (Wilkinson, 1972). The total thickness may be as much as 3000 m (Beavis, 1976), although the entire Lower Ordovician of Lancefield is only 1900 m thick. Sediment transport direction was mainly to the north and northwest, although east-directed flutes occur in the Romsey Group at Lancefield (VandenBerg & Wilkinson, in prep.). 6

6.5 Heathcote

Belt

The Heathcote Belt (or 'Axis'; fig. 8) is a narrow belt of volcanics and sediments with complex internal structure at Heathcote. A large-scale strike fault (Mount William or Mount Ida Fault( ) separates it from the Melbourne Trough sequence. The oldest rocks (Heathcote Greens tone ) are meta-andesite (at Heathcote) or metabasalt (north and south of Heathcote) with interbedded volcanogenic sediments and shale, intruded by dolerite sills and small, ultramafic pods. The volcanics are metamorphosed to greenschist and prehnite-pumpellyite facies, while the ultramafics are largely altered to talc schist and serpentinite. Minimum thickness is 1800 m at Lancefield (Thomas et al., 1976; Crawford & Keays, 1978). Volcanogenic sandstones within the Heathcote Greenstone contain shelly fossils, including a Protolenid trilobite, indicating Early Cambrian age (P.A.Jell, pers. comm.). A shelly fauna 10)

(Hg)

Victoria

straddling the Early to Middle Cambrian boundary occurs in a small, fault-bounded lens of volcanogenic and calcareous sediment^) at Heathcote (O.P.Singleton, pers. comm.), which may be part of, or post-date, the Heathcote Greenstone. At Lancefield, the volcanics are concordantly overlain by black shale and graded volcanogenic sandstone with late Middle Cambrian dendroids and shelly fossils (Monegeetta Shale^ ), VandenBerg & Wilkinson, in prep.), but at Heathcote the base of the equivalent Knowsley East Formation is faulted out. The overlying Goldie Chert is known with certainty only from Lancefield, and may be faulted out elsewhere. It is overlain with apparent conformity by the Lower Ordovician sequence of the Bendigo Belt (VandenBerg & Wilkinson, in prep.). Small fault blocks of Ordovician (Lancefieldian to Gisbornian(° )) quartzose greywacke and shale occur within the Heathcote Belt near Heathcote (Thomas, 1956). Ms

6.6 Melbourne Trough Belt General limits of the trough are marked by the Heathcote Belt and Djerriwarrh Fault in the (io) j {kg Mount Wellington Belt in the east^ \ The oldest rocks within the trough boundaries are altered andesite, volcaniclastics, shale, and rare infaulted limestone lenses^ \ of probable Early to Middle Cambrian age, outcropping as fault blocks in the Barkly River Belt. Small fault-bounded patches of Lancefieldian shale and chert^ ) occur at Mansfield and Licola. An apparently complete Lower Ordovician sequence^ ™) (La2 to Ya) outcropping in the Mornington Peninsula is broadly similar to that of the Bendigo Sedimentary Belt. The Middle Ordovician to Lower Devonian sedimentary fill of the trough is extremely thick (about 12 km) and almost entirely quartz-rich and continent-derived. The trough comprises two main depositional provinces^ ). The Darraweit Guim Province (western half of the trough) is characterized by rapid sedimentation ending in the Pragian, while the Mount Easton Province (typified by the sequence of the Mount Easton Axis) consists of relatively condensed Middle Ordovician to Pragian, and rapidly deposited Pragian to latest Early Devonian sediments. The Middle and Upper Ordovician of the Darraweit Guim Province consists of a thick sequence (2 km or more) of turbiditic sandstone, mudstone and black shale with Darriwilian (Da3) to youngest Ordovician graptolites (Riddell 'Grits'^ and Bolinda Shale ) outcropping on both sides of the Heathcote Belt and extending westwards to the Djerriwarrh Fault^ ). In the Mount Easton Province, a condensed bl^ck shale (Mount Easton Shale) with Da3 to late Bolindian graptolites, outcrops in numerous fault slivers. The Silurian-Devonian of the Darraweit Guim Province conformably overlies Bolinda Shale, and consists of 9-10 km of predominantly siltstone, with well-marked bands of 'proximal' turbidites, channel-filling sandstone, pebbly mudstone and conglomerate in the upper Llandoverian (Sp, lower part of Ac) and in the Lower Devonian north of Lilydale. Facies changes first become evident in the Upper Silurian and become more pronounced in the Lower Devonian sequences. At Heathcote and Kinglake-Lilydale, a gradual upward increase in abundance and diversity of shelly fossils points to gradual shallowing, culminating in deposition of the very shallow water Lilydale Limestone at Lilydale and of cross-bedded pebbly sandstone at Heathcote. Contemporaneous sediments at Seymour and Yea are deeper-water turbidites and mudstones. Sandstones and mudstones are of a sedimentary-granitic provenenace, but conglomerates contain a greater variety of clast types, including chert, reef quartz, rhyolite (?), limestone and rare schist in the Springfield Formation, and granodiorite and probably other igneous rocks in the Lower Devonian Broadford Conglomerate at Yea and Seymour. Flute casts indicate transport to the east, northeast and north. In the Mount Easton Province, the Jordan River Group (late Llandoverian to Pragian) is in fault contact with the Mount Easton Shale and is about 2200 m thick (VandenBerg, 1975), i.e. west

a n c

(Ub)

Victoria

only about a quarter as thick as contemporaneous sediments farther west. It comprises banded, massive and bioturbated siltstone units, quartz-rich turbiditic sandstone units, and a thin but very extensive black shale (Wilson Creek Shale) at the top. Shallow-water sediments are known only from a small area at the southern extremity of the Mount Easton Axis and were probably deposited on a local structural high. They consist of mudstone, volcanogenic sandstone and conglomerate (Boola Formation), with clasts of Cambrian metabasalt and Devonian limestone probably derived from the Waratah Bay belt. The overlying Coopers Creek Limestone appears to grade laterally into Wilson Creek Shale. The Walhalla Group (Pragian to latest Early Devonian?) is more than 5000 m thick and comprises a lower unit (Norton Gully Sandstone) with abundant 'proximal' turbidite sandstone and channel and slump conglomerates, and an upper unit of thin-bedded siltstone and sandstone (Montys Hut Formation; VandenBerg, 1975). Gross distribution of the Norton Gully coarse clastics suggests transport to southwest and west, with the source area most probably lying to the east of the trough. The youngest strata are the Cathedral Beds, a 2-4 km thick regressive sequence preserved in plunging synclines around the Cerberean and Acheron Cauldrons. It consists of a massive siltstone with peculiar cavities, and sandstone, partly of 'redbed' type, with cross lamination, ripple marks, and occasional mudcracks. The age may be latest Early or earliest Middle Devonian. The strata of the easternmost part of the Melbourne Trough are the Mount Useful Slate, here regarded as correlative of the Mount Easton Shale and Jordan River Group. The Jordan River Group correlative consists of banded and bioturbated siltstone, locally with abundant evidence of slumping (Donnellys Creek Siltstone) and turbiditic sandstone units ('Selma Sandstone', 'Serpentine Creek Sandstone', etc.) whose stratigraphic relationships are not known. The rocks are metamorphosed to slate and phyllite of greenschist facies, and show up to three deformations. The main deformation produced asymmetric to recumbent folds with west-dipping axial planes, commonly with metamorphic layering along the cleavage. Later deformation produced west-dipping thrust faults, and fine crenulation and chevron-type folds in the firstformed cleavage (Cochrane & Roberts 1975). 6.7 Mount Wellington and Waratah Bay Belts

These are narrow belts of greenstone and sediments with complex structure and large time gaps between successive units. The belts are here regarded as separate structures, with the Waratah Bay Belt possibly representing a southern extension of the Mount Easton 'Axis' of the Melbourne Trough. The oldest rocks are greenstone complexes of probable Early Cambrian age, consisting of thick piles of metabasalt, volcaniclastics, shale and chert( ' ), intruded first by dolerite sills, and later by ultramafic and gabbroic rocks^ ). The volcanics are metamorphosed to prehnite-pumpellyite or greenschist facies, while the ultramafics are largely serpentinized. Fossiliferous Cambrian rocks are known only from Wellington River, where altered ultramafics are unconformably overlain by graded sandstone, siltstone and a basal conglomerate, all derived from the ultramafics (Garvey Gully Formation; Teale 1920; I.R.Duddy, pers. comm.). An interbedded, partly sheared-out band of limestone (Dolodrook Limestone) contains latest Middle to early Late Cambrian shelly fossils. At Waratah Bay, small lenses of unfossiliferous recrystallised limestone faulted into the volcanics may be of Cambrian age. The Ordovician is represented by three main units. At Waratah Bay, limestone and calcareous mudstone with Tremadocian shelly fossils (Digger Island Formation) is faulted against Cambrian volcanics. At Howqua River, black shale and siliceous shale with Lancefieldian (La2) graptolites are faulted between Cambrian volcanics to the west, and a turbiditic sequence with Bendigonian graptolites (Ho) to the east. The third unit is the Mount Easton Shale, which appears to be more Ja Wa

Victoria

condensed than farther west and includes chert bands. It occurs as large and small fault slivers within and around the margins of Cambrian rocks at Wellington River and Howqua River, and immediately west of the Waratah Bay belt, and contains Darriwilian (Da3 or older) to late Bolindian graptolites. Quartz-rich sandstone, mudstone and shale of supposed Early Ordovician age at Tatong have recently been found to be at least in part Silurian-Devonian (McGoldrick & Gleadow, 1968). Thomas (1959) however recorded a small patch of black shale with Castlejnainian graptolites near Dookie, faulted against Cambrian rocks. The Waratah Bay Belt contains two Lower Devonian limestone formations; the older (Waratah Limestone, ) lies directly on Cambrian volcanics, and underlies the younger (Bell Point Limestone, P) with a gently unconformable contact. Wr

6.8 Eastern Victoria The sequence of Eastern Victoria comprises terrigenous clastics and carbonates ranging from Early Ordovician to latest Early Devonian, and volcanics of Early or Middle Silurian and Early Devonian age. The oldest beds are Bendigonian, and are known from two localities. One, in the upper Howqua River, is at the base of a sequence of turbiditic quartzose greywacke and mudstone, faulted against Howqua Shale to the west and against graptolitic Darriwilian and Gisbornian black shale and sandstone to the east. The other, recently discovered locality is at Eskdale in the Mitta Mitta Valley, and consists of metamorphosed black slate with Tetragraptus fruticosus (4-br.), T. acclinans, and Didymograptus sp. (Kilpatrick & Fleming, 1980). The remainder of the basement of Eastern Victoria is a thick, poorly fossiliferous turbiditic sequence of quartz-rich sandstone and mudstone with rare black shale and chert (Hotham Beds). Graptolites range from late Darriwilian to early Bolindian west of the Kiewa Fault, and from Gisbornian to late Bolindian farther east, but the presence of early Bendigonian graptolites in the middle of the belt at Eskdale suggests that a considerable portion of the sequence may be Early Ordovician. The strata are partly converted to slate and phyllite, and more locally to high-temperature schist and migmatitic gneiss of hornblende hornfels to amphibolite facies (Omeo Metamorphic Complex). The metamorphism antedates the Silurian rocks. The latter are confined to complex graben structures (Cowombat Rift) extending from Eustace Gap to Bindi, Nowa Nowa and Co wombat Plain, and small outliers occur between Yalmy River and Sardine Creek. The sequences of the Wombat Creek and Reedy Creek Grabens are broadly similar, with thick, ignimbritic, probably partly marine acid volcanics (Mitta Mitta and Thorkidaan Volcanics) overlain by shallow marine to partly turbiditic clastics with limestone bands and lenses (Wombat Creek and Enano Groups). The Enano Group contains a significant proportion of dominantly acid volcanics. Both groups contain Late Silurian shelly fossils (Bolger, 1974; VandenBerg et al., 1982). The Silurian rocks of the Co wombat Rift are strongly cleaved and foliated, and have been extensively metamorphosed to greenschist facies. Recent mapping by VandenBerg and others has shown the existence of a thick marine sequence of Early Silurian age (Yalmy Group) in the Deddick River - Yalmy River area of East Gippsland (VandenBerg, 1981). It overlies a condensed Upper Ordovician (early Gisbornian to late Bolindian) black shale (Warbisco Shale) with concordance although contacts are invariably faulted. The Yalmy Group comprises three units: a lower shallow marine coarse sandstone derived from a newly emerged granitic source; a middle banded silts tone containing a graptolite fauna which correlates with the British Zone of M. convolutus, and an upper unit of turbiditic very fine quartzite. The sequence is several thousand metres thick and is folded about widely

Victoria

spaced, open folds which trend predominantly east-west. Slaty cleavage is absent from both the Yalmy Group and Warbisco Shale, but is well-developed in the (Middle to Lower Ordovician?) turbiditic sediments underlying the Warbisco Shale. Lower Devonian rocks are contained in a broad, open synclinal structure, superimposed on the Silurian and older rocks between the Indi River and Nowa Nowa (Buchan 'Rift'; VandenBerg et al., 1982); in smaller structures at Bindi and Errinundra; in a deep south-plunging syncline at Tabberabbera; in a small cauldron subsidence near Walwa; and in the northern part of the Wombat Creek Graben. The Buchan 'Rift' is occupied mainly by Snowy River Volcanics and Buchan Group, but near Gelantipy the volcanics are underlain with slight unconformity by the Seldom Seen Group, 2300 m of chert and quartzite conglomerate, sandstone, and mudstone with one interbedded rhyodacite. The Snowy River Volcanics are up to 3 km thick and show marked thinning at their western boundary (Lenard, 1976). In the outlier at Bindi, only the thin topmost units are represented (VandenBerg et al., 1982). The rocks in the northern part of the Wombat Creek Graben, formerly included in Mitta Mitta Volcanics, are now considered to correlate with Snowy River Volcanics (Bolger, 1979). The group is stratigraphically complex, with numerous sedimentary units separating volcanic units. The volcanics are mostly subaerial, and comprise ignimbritic rhyodacite and rhyolite, flow-banded rhyolite, and some andesite. Sediments include conglomerate, tuff, mudstone, shale, and chert. Marine shelly fossils occur near the base of the group at Mount Tara (Cochrane & Samson, 1950) and near the top at The Basin (Bradley, 1969). The most complete Buchan Group sequences are preserved in structural depressions at Buchan and Bindi, but smaller, partly fault-bounded patches are scattered over a large area, between Co wombat Plain, Errinundra, and South Buchan. The contact with the underlying Snowy River Volcanics is very slightly disconformable at Bindi and Buchan. The Buchan Group consists of up to 950 m of shallow marine limestone, nodular limestone and calcareous mudstone, with volcaniclastic sediments at the base. Rich shelly and conodont faunas indicate Emsian age (see VandenBerg et al., 1976). The Wentworth Group at Tabberabbera consists of more than 1500 m of richly fossiliferous shallow marine sandstone, siltstone, conglomerate and subordinate limestone with faunas indicating probably Emsian age (Talent, 1963). It overlies Hotham Beds with a strong angular unconformity. The Jemba Rhyolite near Walwa occupies a medium-sized cauldron subsidence surrounded by a ring dyke, and consists of 650 m of ignimbritic rhyolite which has given a Rb-Sr age of 408 ± 8 Ma (Brooks & Leggo, 1972). 6.9 Tectonic history and palaeogeography

(Tables 1 & 2)

The narrow Cambrian belts of Heathcote, Mount Wellington, Waratah Bay, and perhaps Mount Stavely, have clearly played a major role in the tectonic development and palaeogeographic history of Victoria. They are structurally complex faulted belts and are, as yet, relatively poorly understood. The Heathcote and Mount Wellington Belts form structural and, in a broad sense, depositional boundaries to the Melbourne Trough. The Waratah Bay Belt formed a depositional high in earlier Ordovician and throughout Early Devonian times, and a portion of the Mount Wellington Belt at Dolodrook may have been a high during the Cambrian and Early Ordovician, but the northern portion of Howqua River, and the whole of the Heathcote Belt, appear to have remained depressed for much of Cambrian and Ordovician times. Although it is reasonable to assume that the Cambrian rocks of western Victoria represent the fill of a Cambrian trough, whose eastern limit lay somewhere between the Heathcote Belt and the Ballarat-Wedderburn Line, the history of this trough is almost unknown. The Glenelg River

Victoria

BELT

STAWELL SED,

BELT

| <U

BENDIGO

£ 'S

SED.

HEATHCOTE BELT

S T A V E L Y BELT

GLENEL6 SED.

C S3 jQ S. 0)

BELT

TROUGH BELT

EASTERN

VICTORIAN

BELTS

VENTWORTH

BUCHAN

GROUP

"RIFT"

M E L B O U R N E

DEVONIAN

GRAMPIANS SILURIAN

MELBOURNE

1X3 CO

LOWER

MT W E L L I N G T O N BELT

Table 1 Schematic Time-space plot for Victorian early Palaeozoic sedimentation.

COWOMBAT T R O U G H

"TROUGH"

"RIFT"

(?RI FT) t |

UPPER ORDOVICIAN

MIDDLE

LOWER

CAMBRIAN

not

? ? exposed

not preserved

1 |

S T A W E L L

T R O U G H

T R 0 U iG H

| ?

chert

not

shale and voicejnicla s t i e s

? not

limestone and volcaniclastics

exposed

exposed volcanics

T R O U G H

B E N D I G O

G L E N E L G

shale

W A G G A

not preserved

v<)lcani cs

? not exposed

volcanics

Explanatory Notes for Table 1. 1. 'Stawell Trough' has been shown across Mount Stavely Belt in the absence of any evidence that it represents a major partition of 'trough' sequences. 2. Bendigo Trough: (a) Western limit of Lower Ordovician shown extending west of 'Ballarat-Wedderburn Line' as suggested in Tectonic History and Paleogeography discussion. (b) Eastern limit shown crossing into Eastern Victoria (across Mount Wellington Belt) as suggested by the Lower Ordovician sequence east of Howqua River segment of Mount Wellington belt. Probably safe to assume basement at least as old as Early Ordovician in Eastern Victoria. (c) 'Axial' belts shown as non-active in Eariy Ordovician. So far, evidence of Early Ordovician uplift is only known from Waratah Bay, which may not represent E margin of Melbourne Trough - probably trends north into 'Mount Easton Axis'. Shallow-water sedimentation in Middle Cambrian may have extended across the entire region, i.e. not confined to presently exposed 'axes' as far as we know. 3. Melbourne Trough: (a) Shown as beginning in Gisbornian since that is when a drastic facies change can at least be documented across the Mount Wellington Belt. It is of course a rather subjective judgement where exactly one places an age boundary between two superimposed troughs in a conformable succession, but the Darraweit Province/Mt Easton Province contrasting styles of sedimentation can be seen already in the Late Ordovician, and lasted into mid-Early Devonian. (b) Upper Ordovician 'Melbourne Trough' style of sedimentation shown extending well to west of Heathcote Belt. The fact that many of the granites in the Bendigo Sedimentary Belt are known to intrude rocks as young as Darriwilian suggests a substantial Upper Ordovician cover across much of this belt, and invalidates Beavis' (1967) argument that sedimentation shifted eastwards with time. Youngest preserved sediments do not prove cessation of deposition. Also, the deformation/cleavage development is of a style which one would expect to form at depth. 4. In line with 'trough' designation of 'trough' sequences, Eastern Victorian Silurian and Lower Devonian are designated 'rifts'. Wentworth Group could be designated 'Wentworth Basin'.

Victoria

Table 2 Tectonic, metamorphic and igneous events in Victorian Devonian in relation to sedimentation. Ma MELBOURNE

2 : <C

HOWITT

Famennian

LLJ Q

Numerous high level plutons,

volcanics.

Numerous dates within

Ordovician + Avon River sediments

range 360 - 375 Ma.

Frasnian CERBEREAN/ACHERON

and other

AVON

cauldrons including Snobs Creek Volcanics (dated 367 - 5 Ma). Rhyol ite, dacite,andesite,ignimbrite. Basal and interbedded sediments. Z C

Givetian

TABBERABBERAN

Z O >

Woods Point dike swarm

(373 - 389 Ma dates)

_l O O

OROGENY

TABBERABBERAN

LLJ

Gedinnian

VICTORIA

360

Angusvale

COMPLEX

Kameruka Granodiorite(381-7 Ma)

Diorite dike swarm.

: Phase 1.

VOLCANIC

Non-marine trough sediments. Acidic and some mafic volcanics. Fish and - 380 plant remains. Unconformable on Ordovician and granite.

Uplift, erosion, unroofing of granites.

(380 - 390 Ma dates)

OROGENY

granites intrudinq volcanics. BOYD

granitic plutons

Bega Batholith Granite plutons (386 - 392 Ma) - 3 9 0 intruding Ordovician beds.

Strong folding, metamorphism, uplift.

WENTWORTH

GROUP

BUCHAN

GROUP

Marine quartz sandstone, siltstone limestone and conglomerate. Unconformable on Ordovician.

Marine mudstone and limestone. Unconformity at base.

BOWNING OROGENY : Phase 2. (Bindian)

Block-faulting, mild folding, erosion. Snowy River Volcanics Calc-alkaline rhyolite to dacite

Older marine units of Melbourne Trough.

GROUP

Mt Buller, Mt Stirling

<ii Emsian WALHALLA GROUP 0> Norton Gully Sandstone and Monty's 0 Hut Formation. SIEGENI AN O

: Phase 2.

and related

COUVINIAN Cathedral Beds: Marine quartz sandstone and siltstone

RIVER

Thick non-marine sediments with numerous acidic volcanics, including cauldrons. Internal disconformities.Fish & plant remains.

Intermediate - mafic calc-alkaline dikes, strongly differentiated.

SOUTHEASTERN

MERRIMBULA GROUP: Non-marine quartzose sediments. No volcanics. Fish and plant remains.Invertebrates, 1n marine intercalation. Block-faulting, mild folding, erosion, unroofing of granites. | - 370 Warby Range Granodiorite (375-6Ma) Gabo Island Granite (363 - 12 Ma) Subvolcanic pluton intruding High-level subvolcanic alkaline

commonly intruding cauldron

TROUGH

MANSFIELD GROUP: Non-marine red-bed sequence fining upwards. Fish and plant remains.

POST TECTONIC GRANITES

0 >

Q_ Q_

TROUGH

Conformable with Silurian. BOWNING OROGENY

Phase 1.

-400

Unconformable on Silurian. Strong folding,metamorphism,unroofing of granites.

410

Beds west of the Mount Stavely Belt differ from the St Arnaud Beds east of it in that they contain rare carbonate and volcaniclastics; other than that, they are like all trough sediments in Victoria in being quartz-rich and continent derived. The Glenelg River Beds were deformed in or before the Early Ordovician, probably during the Delamerian Orogeny. The deformation of the St Arnaud Beds may be Early Ordovician (Delamerian) or Early Silurian (Benambran), or both. Regional strike is northwest, and at least two folding events are recognised. The Lower Ordovician turbidite sequence of western and central Victoria occupies the broad Bendigo Trough. Its western boundary lay between the Mount Stavely Belt and the BallaratWedderburn Line, but relationships with the underlying Cambrian are not known. Deposition extended across the future Heathcote Belt, Melbourne Trough and Mount Wellington Belt and probably across most of Eastern Victoria. West of the Heathcote Belt, the sediments have been tightly folded about near-vertical, generally NNW-trending axes and are strongly cleaved. From the beginning of the Late Ordovician, the Mount Wellington Belt formed the site of a strong facies change, indicating that the Melbourne and Wagga Troughs had become distinct basins at this time. In the Melbourne Trough, subsidence and deposition were most rapid in the western part (Darraweit Guim Province) in Late Ordovician, Silurian and Early Devonian time; the sediments were derived from the south and west - probably from the folded and uplifted Bendigo Trough sequence. In the eastern part (Mount Easton Province), condensed sedimentation in the Late Ordovician, Silurian and Early Devonian was followed in the late Early Devonian by rapid deposition of thick coarse turbidites and ended with minor shallow-marine and probably non-marine sedimentation. Folds in the western part of the trough are relatively open, widely spaced, and follow arcuate trends; slaty cleavage is generally absent. Towards the east, folds become tighter and closely spaced, and have a fairly uniform NNW trend. Strike faulting becomes important,

Victoria

especially along the line of the Mount Easton Belt (a structural high with a core of Ordovician rocks) and in the Mount Useful Slate Belt. Slaty cleavage is developed in much of this eastern part. Most folding and faulting took place in the Middle Devonian Tabberabberan Orogeny, with some further deformation in the Early Carboniferous. In western Victoria, in Silurian time, a broad, rapidly subsiding synclinal basin (Grampians Trough) was filled with rhyolites and a thick deltaic quartz-rich sequence, derived largely from the south (Grampians Group). The sediments were mildly deformed before emplacement of Devonian granites. The extensive and thick Middle to Upper Ordovician turbiditic sandstone-mudstone sequence of eastern Victoria (Hotham Beds) is contained in the Wagga Trough. No palaeocurrent data are available, but the sediments clearly could not have been transported across the black shales of the Mount Easton Province to the west - their most probable source lay to the south. The trends of folds in the Hotham Beds varies from predominantly northwesterly west of the Kiewa Fault, to northeasterly east of it, with local latitudinal trends. Open folds with near-vertical axial planes appear to predominate, but recumbent isoclinal folds, occasionally with near-horizontal axial planes, have been recorded from Tabberabbera (Murphy, 1979) and Ensay (Joyce, 1979). The folding and subsequent regional metamorphism of the Hotham Beds occurred during the Early (?) Silurian Benambran Orogeny, after which the rocks formed a relatively stable basement for a new pattern of deposition. The Co wombat 'Rift' probably formed as a response to large-scale crustal fracturing and wrench faulting, producing deep grabens in which thick Silurian acid volcanic and shallow marine to turbiditic sequences were deposited (W. J.R.Blake, pers. comm.). The effects of the Early Devonian Bindian ( = Bowning) Deformation were most strongly felt in and along the margins of the Co womb at Rift, and involved lateral displacement along the graben margins, and strong compression of the rocks within the grabens. The Bindian Deformation (Bindi Orogenic Phase of Packham, 1969) is best shown at Bindi, where Snowy River Volcanics overlie strongly foliated Silurian volcanics with angular unconformity, along which a Palaeozoic soil is preserved (VandenBerg et al., 1982). Folding within and along the margins of the Reedy Creek Graben is complex, with folds trending roughly parallel to the graben margins, and fold styles ranging from open with near-vertical axial planes, to isoclinal recumbent. Prominent crenulation suggests multiple folding, due at least in part to wrench faulting along the graben margins. Further crustal extension in the Early Devonian produced the Buchan 'Rift', in which deposition of thick acid ignimbrites and predominantly non-marine clastics (Snowy River Volcanics) was followed by deposition of a widespread shallow marine limestone and mudstone sequence (Buchan Group). A separate basin at Tabberabbera received a shallow marine fan sequence, probably derived from the NW (Murphy, 1979). Deformation during the Middle Devonian Tabberabberan Orogeny was most severe in the soft Wentworth and Buchan Group sediments, where it produced open, north-trending folds with mostly near-vertical axial planes, and reticulate cleavage. Block faulting also occurred, and renewed right-lateral displacement along the Indi Fault imposed strong foliation on adjacent Snowy River Volcanics. Granite emplacement accompanied each of the three orogenic pulses. Benambran granitoids are often strongly foliated, have aureoles of high-grade metamorphics, and have yielded a few KAr ages of 430-434 ± 17 Ma (Richards, & Singleton, 1981). Clear distinction between Bindian and Tabberabberan intrusions is usually only possible where stratigraphic constraints are present, for example, the Bindian Forlorn Hope Granodiorite, which intrudes Enano Group and underlies Snowy River Volcanics, and the Tabberabberan Angusvale Diorite and Mount Taylor Porphyry, which intrude Wentworth Group and underlie Upper Devonian sediments.

New Zealand

7. NEW ZEALAND Late Precambrian to Devonian rocks of New Zealand are confined to the western part of the South Island in West Nelson, Westlaiid and Fiordland extending eastwards on to the Southern Campbell Plateau and north along the Tasman margin (Fig. 1). In the West Nelson-Westland region, strata are distributed in three main, meridional belts (Grindley, 1961; Cooper, 1979a) and it is convenient to discuss the sequence in terms of the three belts. It is clear that the three belts represent at least two distinct depositional troughs or regions but the original relationships of the regions are not yet certain (Fig. 10). 7.1 Western Sedimentary Belt The oldest known rocks in New Zealand are paragneisses within a granite-gneiss complex, the Charleston Metamorphic Group ( Constant Gneiss, Charleston Gneiss, of some authors) at Charleston on the west coast; a 680 ± 21 Ma Rb-Sr isochron date has been recorded by Adams (1975). The gneiss could well be part of a Precambrian continental basement underlying the Western Sedimentary Belt sequence. The sedimentary sequence is quartz-rich and continent-derived (Nathan, 1976) and ranges from Late Cambrian to Late Ordovician in age (Cooper, 1979a). Quartz-rich sandstone and muds tone predominate; volcanics and limestones are almost entirely absent. The oldest known sediments, the Greenland Group of Cambrian to Early Ordovician (Rb-Sr dates of 490-510 Ma) age form a remarkably uniform suite of alternating sandstone and mudstone. Poorly sorted sandstone predominates with quartz comprising 70-95% of the sand fraction (Laird 1972). Graded bedding, directional sole marks, load casts and flame structures are widespread and the beds have been interpreted by Laird (1972) and Laird & Shelley (1974) as a turbidite succession. Thickness is likely to be several kilometres. To the east of the Karamea granite-granodiorite-tonalite batholithic complex (SilurianCarboniferous; Karamea Batholith of Fig. 10) is a sequence of quartz-rich sandstone, mudstone and black (graptolitic) shale. In the Aorangi Mine area the oldest beds are alternating sandstone and mudstone (Webb Formation) inferred to be of earliest Ordovician age and possibly the lithostratigraphic equivalent of the Greenland Group. They are conformably overlain by siliceous black shale and chert, quartz sandstone and mudstone (Aorangi Mine Formation) with abundant graptolites representing the Lower Ordovician Adelograptus (La2) to Oncograptus (Ya2) zones. Overlying beds are quartz-sandstone, alternating sandstone and mudstone and black shale (Slaty Creek Formation) with Middle to early Upper Ordovician graptolites (Dal - Gil zones). The youngest beds are laminated siltstone, sandstone and minor black shale (Formation A, informal) with early Late Ordovician (Gil zone) graptolites and trilobites. Full thickness of the Aorangi Mine sequence is at least 3700 m. To the south, in the Cobb Valley - Roaring Lion area is a sequence equivalent to that of the Aorangi Mine area (Leslie, Douglas and Peel Formations, Grindley, 1980.) At Reefton, Lower Palaeozoic rocks (Greenland Group) are overlain with inferred angular unconformity by a sequence of quartz sandstone, mudstone and muddy limestone (Reefton Group Suggate, 1957), of Lower Devonian (middle to uper Pragian) age (Allan, 1947; Strusz, 1972).

New Zealand itPE

^ 9 M t Burnett

Aorangi Mine

41 S—

GOLDEN BAY Separation Point

IIIV Parapara\v\~. l l l l k I

Mt Olympus'

P e a k

/Haupir^^^^^' |li Range Anatoki l|Range||^^ | P 1 Devil I Range JKnnnx;

t ASM AN: "MOUNTAINS;

KHailes^rW

j^Riwaka River i Motueka

Mt Lodestone

Karameal

Mt Arthur

Mt P a t r i a r c h ^ *

Western Sedimentary Belt Central Sedimentary Belt Eastern Sedimentary Belt Felsic Intrusives Riwaka Complex m a f i c - ultramafic belt

Mt Oweru Reefton

/ 6 0 km Fig. 10

25 Km

Springs Junction 8 0 km

Simplified geological map of Northwest Nelson region, New Zealand, showing major early Palaeozoic sedimentary belts, later Palaeozoic and Mesozoic intrusive complexes and major late Cainozoic transcurrent faults. (After Cooper, 1979a, Fig. 3, with modifications). Post-Devonian covering strata omitted.

50 7.2 Eastern

New Sedimentary

Zealand

Belt

Limestones, mudstones and quartz-rich sandstones range from Middle Ordovician (or older) to Early Devonian in age. Rapid lateral fades change is common. The oldest beds are the phyllitic, calcareous and dolomitic muds tone and quartz sandstone, at least 1200 m thick (Owen Formation) underlying the thick limestone/marble unit at Mount Owen. The top of the limestone, referred to as Arthur Marble 1, contains late Middle Ordovician (Llandeilo) conodonts at Mount Arthur and Mount Owen, and the Owen Formation is therefore Middle Ordovician or older. At Mount Owen, the limestone has suffered extreme internal deformation; original thickness is uncertain but is likely to be of the order of at least several hundred metres (Coleman, in press). Between Mount Owen and Graham Valley, Arthur Marble is conformably overlain by quartz-rich sandstone and mudstone with less common black shale (Wangapeka Formation) containing Eastonian graptolites and, in the south, about 1500 m thick. In Graham Valley, Wangapeka Formation is overlain by a second limestone unit referred to as Arthur Marble 2. At Hailes Knob this unit contains Bolindian corals and conodonts; it is tectonically thickened and probably was of the order of 500-1000 m thick. Elsewhere, however, Wangapeka Formation passes conformably up into the Silurian Hailes Quartzite; Arthur Marble 2 thus appears to be the lateral equivalent of the upper part of the Wangapeka Formation or, less probably, of the lower part of Hailes Quartzite. The change to quartz-sandstone deposition (Hailes Quartzite) takes place at about the base of the Silurian. Muddy sandstone and clean quartz sandstone are the dominant lithotypes in the unit which contains middle Silurian brachiopods at Mount Gomorrah (M.Garratt, pers. comm.) and a Pridolian or lower Lochkovian Notoconchidium fauna at Wangapeka Valley. At Hailes Knob the quartzite conformably overlies Bolindian Arthur Marble 2; it is therefore thought to span the Silurian Period (Cooper & Wright, 1972). Near Mount Gomorrah, Hailes Quartzite is overlain by phyllitic siltstone with thin fine sandstone beds (Fowler Formation) at least 450 m thick. The unit is unfossiliferous and is thought to be of early Devonian (early Lochkovian) age (Coleman, in press). The youngest beds in the eastern belt are the thick sequence of mudstone, muddy sandstone with less common sandstone and limestone (Baton Formation) in Baton and Wangapeka valleys. A rich brachiopod assemblage of late Lochkovian to early Pragian age (Strusz, 1972; late Siegenian to early Emsian - Shirley, 1938) is known from several hundred metres above the base of the formation, which was estimated by Willis (1965) to be about 2600 m thick. In the Skeet River - Moran Creek area the formation rests with angular discordance on Wangapeka Formation (Coleman, in press). A basal conglomerate in the Baton Formation contains Haupiri Group (Central Sedimentary Belt) detritus. An interval of folding and erosion is thus implied in the Early Devonian (Lochkovian) epoch (Grindley, 1978b). At Springs Junction, ankeritic and volcanogenic sandstone, siltstone and conglomerate with Late Cambrian trilobites is overlain by limestone with Middle Ordovician (Llanvirn and Llandeilo) conodonts, which in turn, is overlain by slate and sandstone with Late Ordovician (late Gisbornian or Eastonian) graptolites (Cooper 1979a).

7.3 Central Sedimentary

Belt

Ranging from latest Precambrian (Vendian) or Early Cambrian to Middle Ordovician, the central belt sequence is dominated by volcanics, and volcanogenic sediments. Lateral thickness and facies variations are common. Extreme structural complexity makes stratigraphic interpretation difficult (Grindley, 1961, 1971, 1978a, 1980). The oldest strata are dark siliceous and arkosic, micaceous, pyritic and commonly ankeritic sandstone, mudstone and diamictite with thick interbedded chert bodies (Balloon Formation). Acid volcanics and limestone lenses are

New

Zealand

rare. The sequence has suffered widespread autobrecciation and soft sediment deformation producing a range of textural types including diamictite (Grindley, 1980). Acritarchs are known from several localities and suggest that the formation may, in part, be Early Cambrian or ?Vendian in age. Overlying the Balloon Formation conformably in Cobb Valley is a thick (1-3 km) pile of spilitised mafic to intermediate volcanics, flows, shallow sills, tuff, volcanic sandstone and siltstone (Devil River Volcanics), deposited mainly in a marine environment (Grindley 1971, 1980). Associated with the volcanics in Takaka Valley is a small ultramafic complex (Cobb Igneous Complex; Hunter, 1977) of serpentinised dunite-peridotite, orthypyroxenite, websterite and gabbro. Emplacement predates deposition of Lockett Conglomerate (Hunter, 1975). Devil River Volcanics are overlain by siliceous, laminated siltstone and sandstone with lenses and beds of limestone (Tasman Formation). Late Middle Cambrian (Ptychaqnostus punctuosus P. nathorsti Zones) trilobites are known from several of the lenses and from shales (R.A.Cooper, in prep.). Other fossils include inarticulate brachiopods, ostracods, and conodonts (D.I.MacKinnon, pers. comm.; Henderson & MacKinnon, 1981). Thickness ranges from 200 to 500 m. In Cobb Valley, Tasman Foration is conformably overlain by a thick unfossiliferous fanglomerate (Lockett Conglomerate) derived entirely from older Central Belt formations (particularly Devil River Volcanics, and Balloon Formation). Thickness ranges from 0 to 1000 m. Locally, the conglomerate rests directly on Balloon Formation with strong angular discordance. The conglomerate passes upwards and laterally into ankeritic and volcaniclastic sandstone and siltstone with conglomerate lenses, volcanic flows and sills (Anatoki Formation). A possible equivalent of this unit at Springs Junction contains Upper Cambrian trilobites; otherwise age diagnostic fossils are unknown in both Anatoki and Lockett Conglomerate Formations. Thickness of the Anatoki Formation is at least 1300 m near Boulder Lake (Brathwaite, 1968), and 1500-2000 m in the Mount Patriarch area (Coleman, 1977). Conformably overlying Anatoki sandstones in the Mount Patriarch - Crow Valley area are calcareous siltstone and sandstone with minor limestones (Patriarch Formation), about 400 m thick (Coleman, 1977). Lateral variation in lithology is marked. Tremadocian trilobites are known at several localities. The unit is overlain by dark impure flaggy limestone and sandy and pure partially dolomitised limestone (Summit Limestone), at least 370 m thick and with earliest Arenigian conodonts and trilobites (Cooper & Druce, 1975). Unfossiliferous shales (Baldy Formation) overlie the limestone at Mount Baldy. The younger sedimentary history of the Central Sedimentary Belt is uncertain. At Mount Mytton in Cobb Valley, upper Gisbornian graptolite-bearing shales (Peel Formation; Mount Peel Beds of Keble & Benson, 1929) rest on Summit Limestone with a faulted (thrusted) contact (Grindley, 1980).

7.4 Fiordland Despite widespread metamorphism and intrusion by Devonian-Mesozoic granites, granodiorites, diorites and gabbros, meta-sedimentary and metavolcanic rocks have been recognised in southern Fiordland and along the coast south of Milford Sound. The remainder of central and northern Fiordland comprises a dominantly orthogneissic terrain of intermediatemafic composition, metamorphosed in part to the granulite facies but with widespread retrogression to amphilobite facies producing diorite gneiss as the predominant rock-type (Oliver & Coggon, 1979; Blattner, 1978). These orthogneisses were originally thought to be an integral part of the Early Paleozoic geosynclinal succession (Wood, 1960, 1962, 1966) but are now alternatively regarded as uplifted segments of Precambrian lower crustal rocks of mainly gabbroic

New Zealand composition (Oliver, 1976; Oliver & Coggon, 1979), or as Late Palaeozoic intrusives (Grindley, 1978b). The metasedmientary and metavolcanic supracrustal succession of southern Fiordland resembles the Central Belt rocks of Northwest Nelson, including quartzo feldspathic gneisses and schists, metacherts and quartzites, metaconglomerates, mafic gneisses and marbles. Correlation with Haupiri Group formations of Northwest Nelson has been suggested (Grindley, 1978b). Similar sequences are present along the Fiordland Coast north and south of Milford Sound where the Thurso and St Anne Formations of Wood (1962, 1972) and the Anita Ultramafics are provisionally correlated with the Devil River Volcanics, Anatoki Formation and Cobb Igneous Complex of Northwest Nelson. The Fiordland sequences are extensively disrupted and retrogressed to mylonite and augen gneiss along major branches of the Alpine Fault (Wood, 1972). Similar mylonitic zones are recognised as far south as Dusky Sound. In the far southwest of Fiordland, the Preservation Formation of Wood (1960) is a quartzose sandstone - graphitic shale sequence containing well preserved graptolites of early Ordovician age (Benson & Bartrum, 1935). The relation of this comparatively unmetamorphosed sequence to the higher-grade metasediments to the east is obscured by later faulting and intrusion of early Cretaceous granites. The sequence is faunally and lithologically similar to the Aorangi Mine Formation of Northwest Nelson (Benson & Keble, 1935; Cooper, 1979b). 7.5 Campbell Plateau On the sub-Antarctic Campbell Island, and in offshore wells drilled recently for petroleum, metasedimentary basement rocks have been identified that resemble closely the Greenland and Aorere Groups of Westland and Northwest Nelson, comprising quartzose sandstones, slates and phyllites (Beggs, 1978). The Complex Point Formation of Campbell Island has recently provided Ordovician K-Ar ages of 450 Ma (C.Adams, pers. comm.) similar to those of the Greenland Group (Adams et al., 1974). 7.6 Tasman Margin Metasedimentary rocks have also been identified at the bottom of the Moa-1 oil well off the North Taranaki Coast in the eastern Tasman Sea. They comprise quartzite, calc-silicate schist, and amphibolites closely resembling the Onekaka Schist of Silurian age in Northwest Nelson (see Wodzicki, 1974). Northward continuation of at least the Eastern Sedimentary Belt of Northwest Nelson for another 300 km is indicated. 7.7 Palaeogeography; tectonic, igneous and metamorphic history Two deposition troughs are recognised (Buller Miogeosyncline and Anatoki Eugeosyncline) overlapping largely in age but having dissimilar histories up until the Devonian, when the two were thrust together by the climatic movements of the Tuhuan Orogeny (Grindley, 1978b). 7.7.1 The Buller Miogeosyncline The Buller Miogeosyncline embraces the continent-derived Western Sedimentary Belt which includes the Greenland Group, and possibly also the Eastern Sedimentary Belt. Sedimentary current data indicate derivation from the south and southwest (Laird, 1972). The Charleston Gneiss of the Charleston Metamorphic Group (Nathan, 1978) of the Paparoa Range may form an underlying basement in the southwest (Hume, 1977).

New Zealand

The deformation and low-grade metamorphism of the Greenland Group (Greenland Event; Cooper, 1979a) took place during the late Ordovician - early Silurian as shown by K-Ar wholerock dates on slates of 395-448 Ma (Adams et al., 1974). The folded Greenland Group was invaded by granitic plutons which have given Silurian ages (C.J.Adams, pers. comm.) and uplifted and eroded prior to Middle Devonian transgression by a carbonate-quartzite-shale sequence (Reefton Group). The Western Belt of Northwest Nelson may have been tilted and mildly folded during the Greenland movements. The youngest sediments recorded are of Late Ordovician age (Gisbornian), but these were presumably covered by an appreciable thickness of younger sediments before being overthrust by Central Belt rocks in the Late Silurian - Early Devonian and invaded by Upper Devonian granites. Deformation of the Eastern Belt commenced in the Early Devonian, with recumbent folding and production of transposition cleavage in pelitic rocks and recumbent flow folds in marble and quartzite. Fold axial trends and vergences indicate tectonic transport from south to north (Grindley, 1961, 1971, 1980). The folded Eastern Belt was transgressed in the late Early Devonian by the Baton Formation of late Siegenian - Emsian age, a 1500 m sequence of simplyfolded grey slate, sandstone, minor limestone and conglomerate containing Central Belt detritus (Coleman, in press).

7.7.2 The Anatoki Eugeosyncline The Anatoki Eugeosyncline comprises a Lower Cambrian continental margin clastic sequence, a Middle Cambrian volcanic trough, which subsequently matured into an island arc, an Upper Cambrian flysch-molasse trough and a Lower to Middle Ordovician carbonate-shale shelf. The subsequent sedimentation history is unknown. The early continental margin sequene (Balloon Formation) contains arkosic detritus from a dominantly granitic land mass. Chert pods and lenses, minor tuff and volcanic conglomerate indicate that acid volcanism had already begun in a nearby region. Widespread autobrecciation produced by deformation of unconsolidated sediments suggests precursory tectonic movements. Acid volcanics followed quickly by more mafic volcanics (andesite, basalt and dolerite) suggest rifting of the crust at about the Lower Middle Cambrian boundary (Grindley, 1980). During a major tectonic pulse in the late Middle Cambrian, parts of the Devil River volcanic sequence were uplifted by block-faulting and the underlying Balloon Formation exposed. The block-faulted terrain provided a source-area for the deposition of coarse fanglomerates (Lockett Conglomerate) overlying shales with limestone pods (Tasman Formation). Also during the mid-Cambrian, a layered peridotite-pyroxenite-gabbrodolerite subvolcanic pluton (Cobb Igneous Complex; Hunter, 1977) was emplaced upward into the volanic sequence, with concomitant production of mylonite and cataclasite along its boundaries (Grindley, 1979). Detritus from the complex and its schistose envelope appears in the Lockett Conglomerate. Volcaniclastic and quartzofeldspathic flysch with abundant chert-clast conglomerate and ankeritic sandstone and siltstone (Anatoki Formation) were deposited in the later Cambrian followed by the earliest Ordovician carbonate-shale sequence (Mount Patriarch Group) inferred by Cooper & Druce (1975) to have formed on a shallow offshore rise. Volcanic activity, mainly andesitic, continued through the late Cambrian. Deformation of the Central Belt commenced in the late middle Cambrian (Haupiri Disturbance of Grindley, 1971) with minor thrust movements, accompanying emplacement of the Cobb Igneous Complex, producing mylonite and greenschist (Waingaro Schist), some pebbles of which occur in the Lockett Conglomerate.

54 7.7.3 Tuhuan Orogeny

New Zealand (Devonian)

Interpretation of Tuhuan orogenic events is still controversial partly due to overprinting by later (Mesozoic) structures and partly due to differences in interpretation of complex polyphase Tuhuan structures. In the allochthonous Central Belt hypothesis (Grindley, 1978b) the entire Central Belt sequence was emplaced from the south over the Western and Eastern Belts in a series of nappes in the latest Silurian - Early Devonian. A flat transposition cleavage, a latitudinal lineation, recumbent isoclinal folds verging to the north, and at least four great nappes were produced (Grindley, 1961, 1971, 1978b, 1980). The sequences in each nappe remained predominantly upright but individual tectonic units involve progressively younger rocks from top to bottom suggesting gravitational emplacement (diverticulation). An estimated 5-10 Ma is available for this first (Lochkovian) phase of the Tuhuan Orogeny. In the autochthonous Central Belt hypothesis (Cooper, 1979a), the Central Belt sequence originally underlay the Eastern Belt sequence and formed a positive element during intermittent upward emplacement and eventual overthrusting over the Western Sedimentary Belt. Origin of the nappes, as mapped by Grindley (1971, 1980) and Coleman (in press), is not explained. During this first phase of the Tuhuan Orogeny ( F l ) , no intrusive igneous activity is recorded in the Central and Eastern Belts, but Lower Devonian granites were emplaced in the Western Belt. During the second Middle Devonian phase of the Tuhuan Orogeny (F2), following deposition of the Reefton and Baton River late Early Devonian shelf sequences, a general latitudinal compression produced an array of meridional folds in all three belts, and led to the differentiation of the three belts with the Central Belt remaining in a synclinorial (Grindley, 1978b) or anticlinorial (Cooper, 1979a) position between the Western and Eastern Belts. Many of the thrusts (and recumbent folds) were steepened and acted as reverse or transcurrent faults during this phase. Metamorphism to low greenschist grade accompanied the penetrative Tuhuan movements, but it is difficult to differentiate First and Second Phase metamorphic events. Conspicuous overprinting by higher-temperature regional and contact metamorphism accompanied emplacement of the Tuhuan granites of Late Devonian - Early Carboniferous age in the west and the mafic-ultramafic Riwaka Complex of Late Devonian Carboniferous age in the east. The probably subvolcanic Riwaka Igneous Complex heralded the inception of new crustal rifting and island arc formation associated with the late Paleozoic Mesozoic New Zealand Geosyncline (Grindley, 1974).

Microfossil studies

8. MICROFOSSIL STUDIES A large number of rock samples of inferred late Precambrian to Devonian age from New Zealand, Antarctica and southeast Australia have been processed for acid-resistant, organicwalled microfossils. Unfortunately most were found to contain either no fossils or only poorly preserved and non-diagnostic forms. The following summary outlines those results relevant to the present study; a more complete account will be given separately.

8.1 New

Zealand

The Balloon Formation has yielded the acritarchs Bavlinella faveolata and Trachysphaeridium levis and, as a tentative identification only, the mega-planktic fossil Chuaria circularis. The two acritarch species are known to range in age from Vendian to Early Cambrian (the Scandinavian zone with Schmidtiellus mickwitzi and Holmia mobergi) and suggest that the Balloon Formation ranges in age down to Early Cambrian or Vendian. Chuaria circularis is known only from Upper Precambrian strata and, if its presence could be demonstrated in the Balloon Formation, would afford more positive evidence of a Late Precambrian age (Ford & Breed, 1973; Vidal, 1974). The lower age range of the Balloon Formation is therefore taken in this study as Early Cambrian or Vendian.

8.2 Tasmania Acritarchs considered to be age-diagnostic have been recovered from the inlier of Oonah Quartzite correlate at Dundas, the Dalcoath Quartzite of the Renison Bell sequence, the Duck Bay sequence at Smithton (above, or at the top of the Smithton Dolomite), and the Burnie Formation. The assemblage includes Bavlinella faveolata, Octoedryxium truncatum, Trachysphaeridium timofeevi, T. levis, Pterospermopsimorpha sp., and Churia circularis. O. truncatum is known only from rocks of Vendian age in the Russian Platform, Scandinavia, and Greenland (Vidal, 1976a, 1979a). Its occurrence in Tasmania in rocks with Bavlinella faveolata and the large opaque sphaeromorphs interpreted as C. circularis matches the co-occurrence of the three forms in the Vendian of Scandinavia and Greenland (Vidal, 1979a) and suggests a Vendian age for the units. Other taxa of the assemblage have longer stratigraphic ranges but all are found in the Vendian of Scandinavia and Greenland. The suggested Vendian (whose base is generally taken at about 700 Ma or younger) age for the Burnie Formation is in apparent conflict with K-Ar dates of 725-710 Ma (see note 6, Tasmania) on the Cooee Dolerite which intrudes the formation. However, sediments in South Sweden containing the above diagnostic Vendian taxa have given an Rb-Sr whole rock age of 722 ± 37 Ma. Thus, the Vendian is used here as defined by Vidal (1979b, in press b). Microfossils from the Smithton Dolomite, including Churia circularis, appear to have a late Vendian affinity. The only clearly Cambrian microfossil is from the base of the otherwise barren Crimson Creek Formation at Renison Bell, and consists of a single well-preserved specimen of Baltisphaeridium? strigosum. The species has previously been described from the Lower Cambrian Vergale horizon in Lithuania and from the Rausve horizon in southern Estonia and Latvia (Yankauskas & Posti, 1976). It is also known from the Lower Cambrian of east Greenland (Vidal, 1979a) and from the Lower Cambrian Holmia Series in southern Sweden and southern Norway (Vidal, 1981), and is consistent with an Early Cambrian age for the base of the Crimson Creek Formation.

Microfossil studies

8.3 Antarctica Antarctic results have been outlined by Cooper, et al., (1982) and are summarised below. Age diagnostic microfossils have been recovered from two main areas of outcrop of the Molar Formation of Laird et al., (1982); the first is in the Mount McCarthy area, previously mapped as Robertson Bay Group (Gair et al., 1969) and the second is in the Molar Massif. From the Mount McCarthy area the following taxa were recovered: Bavlinella faveolata, Trachyspaeridium levis, T. timofeevi, Trematosphaeridium holtedahli, Eosphaera cf. tyleri, Protosphaeridium cf. tuberculiferum, Micrhystridiumsp., Vendotaenia sp. and Chuaria circularis?. From the Molar Massif, between Black Glacier and upper Sledgers Glacier the following taxa have been recovered: Bavlinella faveolata, Trachysphaeridium levis, Pterospermopsimorpha cf. densicoronata, Lacunosphaera cf. simplex, Vendotaenia sp., cf. Stictosphaeridium sp., Leiosphaeridia sp., Chuaria circularis? and Archeodiscina umbolunata. The presence of scattered micrhystrids and acanthomorphs in the Mount McCarthy samples and of Archeodiscina umbolunata in Molar Massif are consistent with the upper Lower, or Middle, Cambrian age inferred for these rocks from the occurrence of ptychagnostid trilobites and acrotretid brachiopods in the upper part of the sequence at Molar Massif and Houliston Glacier as discussed above (section 4). However the majority of the taxa, and especially Bavlinella faveolata, are characteristic of older rocks (Vidal 1976a, 1979a) leading Cooper et al. (1982) to infer a Vendian to Lower Cambrian age for the rocks mapped as Molar Formation. However, Bavlinella faveolata and other 'Vendian' acritarchs are now known to range at least as high as the Paradoxides paradoxissimus Zone (Middle Cambrian) in Sweden (Vidal unpubl.). Their occurrence in the Molar Formation is further confirmation of their range into much younger rocks than previously inferred.

8.4 General The acritarch work completed to date is a first reconnaissance study of Australasian and Antarctic rocks. Clearly, there is much refinement and follow-up work to be done, but the results show the potential importance of the group for dating late Proterozoic and early Palaeozoic sedimentary rocks, especially as these units are generally devoid of other fossils and are difficult to date. Unsolved problems arising from the present work are the abundance of morphologically simple acritarchs in the Antarctic Sledgers Group and the apparent lack, or paucity, of microfossils of Cambrian age in Cambrian units throughout the region.

Principal correlations and events

9. PRINCIPAL INTER-REGIONAL CORRELATIONS AND GEOTECTONIC EVENTS 9.1 Age and nature of the Precambrian Basement 9.1.1. South Australia The Archaean to Lower Proterozoic rocks of the Gawler Craton include the Sleaford Complex of southwestern Eyre Peninsula (Thomson, 1980) and the Mulgathing Complex which crops out in the northwest (Daly et al., 1979). Augen and cordierite-garnet gneisses within the layered predominantly metasedimentary Carnot Gneisses (Sleaford Complex) have yielded Rb-Sr total rock ages of 2586 ± 131 Ma and 2412 ± 72 Ma (Fanning et al., 1979) respectively. The latter date probably marks the final stages of granulite facies metamorphism, whilst the older date presumably reflects an unknown preSleafordian orogenic maximum event. According to Webb (1979) the Sleafordian Orogeny took place between 2500 and 2300 Ma ago. However, available evidence suggests that the Sleafordian metamorphism was largely completed prior to 2400 Ma and that granites such as the Whidbey Granite (Rb-Sr date 2350 Ma) were products of the final stages of that great orogenic event. The predominantly acid gneisses of the Mulgathing Complex were formed by granulite facies metamorphism of a sedimentary sequence that included quartz arenites, banded iron formations, carbonates, basic sills and basalts, sometimes pillowed. Metamorphism took place between 2490 and 2420 Ma (Webb, 1979, fig. 2), the younger date being compatible with that obtained for the granulite facies metamorphism of the Carnot Gneisses. The Glenloth Granite, regarded as a late synorogenic granite, intruded the Mulgathing Complex metasediments 2310 Ma ago (Rb-Sr date). Following uplift and erosion, the lower Proterozoic metasedimentary Hutchison Group was laid down unconformably upon the Sleafordian basement. According to Parker (1979) the Group includes a basal quartzite (?Warrow Quartzite equivalent), a sequence of dolomites, iron formations and associated clastics, part of which is equated with the Middleback Subgroup (this contains important iron ores), and an upper pelitic unit, the Yednarie Schist. The Hutchison Group is separated from the predominantly gneissose Lincoln Complex lying to the east by an extensive mylonite zone. Both sequences were deformed and metamorphosed during the Kimban Orogeny which according to Webb (1979, p. 10) commenced about 1800 Ma ago with the formation of granitic gneisses and granulites of the Lincoln Complex. However, Mortimer et al., (1979) have shown that the intrusive Donington Granitoid Suite within the Lincoln Complex crystallised 1813 ± 13 Ma ago and was later subjected to multiphase deformation and granulite and/or amphibolite facies metamorphism during the Kimban Orogeny. According to Webb (1979) most of the Kimban metamorphic activity and synorogenic granite emplacement took place between 1700 and 1580 Ma ago. Minor volcanism represented by the 'Moonabie Volcanics' occurred about 1620 Ma ago. The Kimban Orogeny which terminated 1580 Ma ago gave rise to northeast to north-trending folds in both the basement and Hutchison Group cover. Stratigraphic and tectonic studies have led Glen et al., (1977) and Rutland et al., (1981) to propose that the Hutchison Group was the western portion of a shallow water platform cover that was continuous to the east as far as Broken Hill. However, basement rocks as old as the Sleaford and Mulgathing Complexes are unknown as yet from the Willyama Complex. Post-orogenic granites were emplaced within the Gawler Craton in the succeeding 150 million years. Notable was the widespread predominantly acid volcanism (Gawler Range Volcanics) that blanketed large areas of Eyre Peninsula with ashflow tuffs (ignimbrites) and lava flows, commencing at 1525*15 Ma and possibly extending to 1490 Ma. The volcanics were intruded by the Hiltaba Granite about 1480 Ma ago. K-Ar mineral dates (Webb, 1979) show that retention of

Principal correlations and events

radiogenic argon was not effective until 1450-1400 Ma ago for the Yorke Peninsula portion of the Gawler Craton. Stability of the craton was virtually complete by that date. The pre-Adelaidean Barossa Complex of the Mount Lofty Ranges is exposed in axial culminations and fault zones and is strongly retrogressed giving Rb-Sr metamorphic ages around 850 Ma, but the significance of this figure is not known. No reliable isotopic dates are available for the Mount Painter Complex in the northern Flinders Ranges, but correlation with the Willyama Complex in western New South Wales across the Lake Frome Embayment is generally assumed (Tectonic Map of Australia and New Guinea, Geological Society of Australia, 1971). 9.1.2 Western New South Wales The Willyama Complex, a metamorphic sequence of quartzo feldspathic sediments interbedded with felsic and mafic volcanics has been Rb-Sr dated at approximately 1700 Ma (Pidgeon, 1967), and is intruded by post kinematic granites dated at 1560 Ma. From Broken Hill, metamorphic grade decreases towards the north and northeast from granulite facies through amphibolite facies to greenschist facies. East of the Upper Palaeozoic Bancannia Trough, the Wonominta Complex forms basement to Cambrian sediments and volcanics of the Gnalta region, and is commonly correlated with the Willyama Complex (Pogson & Scheibner, 1976). However, no Adelaidean cover rocks are present, unlike the situation in the Barrier Ranges north of Broken Hill, and the precise age of the Wonominta sediments is uncertain. An alternative correlation is with the Callanna Beds at the base of the Adelaidean Sequence (B. Daily, pers. comm.). An upper age limit is provided by the Mount Wright Volcanics which overlie the Wonominta Complex and have been dated as Early Cambrian. 9.1.3 Antarctica The Nimrod Group of the central Transantarctic Mountains is a 2500 m + sequence of quartzo-feldspathic sandstone, siltstone, limestone, dolomite, quartzite and mafic volcanics all metamorphosed to the amphibolite facies. A three stage deformation history includes early overthrusting and recumbent folding with intrusion of diorite and gabbro, coaxial refolding with migmatisation and partial anatexis, and post-metamorphic open folding and faulting (Grindley, 1972). This complex deformational history has so far resisted resolution by geochronologists using a variety of isotopic methods. U-Pb dates on zircons (Gunner, 1976) point to an Archaean cratonic source region (2800 Ma). Rb-Sr data on selected non-migmatised paragneiss and schist give an isochron at 1980 ± 80 Ma that may be related to isotopic homogenisation during lower Proterozoic sedimentation and diagenesis (Gunner & Faure, 1972). K-Ar data on amphibolites were originally interpreted as indicating isotopic closure at 1000-1100 Ma (Grindley & McDougall, 1969) but subsequent more detailed study (Adams, Gabites & Grindley, 1982) has indicated that isotopic closure was not achieved until the late Precambrian (Vendian - 580-620 Ma) and that excess argon in amphiboles has produced older apparent ages up to 1100 Ma. In the McMurdo Sound region also, late Precambrian metamorphic ages have been obtained on the Olympus granite-gneiss (610 Ma - Faure & Jones, 1974) although older basement units are present (D.N.Skinner, pers. comm.). Metamorphic basement rocks in Northern Victoria Land, between Terra Nova Bay and the Oates Coast west of Rennick Glacier are placed in the Wilson Group (Gair et al., 1969). An RbSr model age of 755 ± 40 Ma (Faure & Gair, 1970) is likely to be a maximum age for the metamorphism. K-Ar age data indicate latest deformation and uplift in the Ross Orogeny( 500 Ma). However, amphibolite clasts derived from the Wilson Group into the Husky Conglomerate of the Bowers Tectonic Zone imply a Vendian or pre-Vendian age for the metamorphism.

Principal correlations 9.1.4

and

events

Tasmania

The Tyennan Nucleus is a metamorphosed sequence consisting largely of interbedded siltstone and orthoquartzite that has been subjected to polyphase deformation in the late Precambrian and early Paleozoic. Rb-Sr data (Raheim & Compston, 1977) have yielded a confusing array of dates, that are believed to reflect four successive deformations, the earliest two of which are Precambrian. The earliest recognisable events (D1-D2) represent prograde metamorphism up to amphibolite facies and penetrative deformation involving early recumbent folds, overgrown on garnet porphyroblasts, and later refolding (Spry, 1962). The post-D2 metamorphic climax is dated by Rb-Sr whole rock isochrons at about 800 Ma (Frenchman Orogeny). Model Rb-Sr dates of about 1100 Ma for some highly radiogenic schists are interpreted as a relict pre-metamorphic age, possibly denoting the time of sedimentation. The Tyennan Nucleus and the very similar Forth Nucleus could thus be approximate correlatives of the Callanna Beds (basal Adelaidean) in an entirely different tectonic setting. 9.1.5

Victoria

East of the Adelaidian sequences of the Mount Lofty, Flinders and Barrier Ranges and the Wonominta Complex, no Precambrian rocks are recognised in the remainder of New South Wales and throughout Victoria. Some S-type granites in southern New South Wales contain zircons dated at 800-900 Ma, probably derived from buried Precambrian basement rocks (Wyborn & Chappell, 1979). Another view is that the Lachlan geosynclinal lower Paleozoic sediments were deposited in a series of eastward-migrating marginal basins, directly on oceanic crust (Packham, 1973; Crook, 1974; Scheibner, 1976), but Rutland (1976) and O.P. Singleton (pers. comm.) believe that Precambrian continental crust extends under Victoria and New South Wales at least as far east as the present continental margin.

9.2 Late Proterozoic 9.2.1 South

sedimentary

cycle

Australia

An extensive platform sequence of late Proterozoic miogeosynclinal sediments was deposited across a broad shelf cut in lower Proterozoic and Archaean basement rocks of the Gawler Craton during the Adelaidean time interval (ca. 1100-1600 Ma). The western portion of the platform Stuart Shelf - received a relatively condensed Adelaidean and Cambrian cover and escaped significant folding at the end of the Cambrian. The Torrens Hinge Zone, a belt of meridional fractures, separates the Stuart Shelf of the more mobile Adelaide Geosyncline, which received an astonishingly thick (24 km + ) sequence of sediments (Thomson, 1969). The Adelaidean sequence is divided into four major groups separated by regional disconformities (Thomson et al., 1976). The Callanna Beds at the base are a sequence of conglomerate, sandstone, quartzite, carbonates and mafic volcanics. The Beda Volcanics on the Stuart Shelf are dated 1076 ±34 Ma (Mason et al., 1978; Thomson, 1980). The Wooltana ( = Depot Creek) Volcanics around the Mount Painter basement inlier in the northern Flinders Ranges are believed to be correlatives but have so far yielded unreliable younger radiometric ages (ca. 750 Ma) possibly due to later thrusting of basement slices into the Callanna Beds. The Wilangee Volcanics near the base of the Adelaidean in the Barrier Ranges north of Broken Hill are probable correlatives. A lengthy erosion interval separates the Callanna Beds from the succeeding Burra Group, which rests directly on gneissic basement rocks in the Mount Lofty Ranges, giving K-Ar metamorphic ages around 870 Ma. The Burra Group contains conglomerate, sandstone, dolomite and siltstone units deposited in a shallow-marine to intertidal environment.

Principal correlations and events

The succeeding Umberatana Group comprises the glacial and interglacial Adelaidean sequences, and is separated by a period of tectonism (Sturtian movements) and erosion from the older Burra Group units. The earlier Sturtian Glaciation contains two tillite units separated by ironstone beds containing drops tones and an internal disconformity. The later Marinoan Glaciation is separated from the earlier Sturtian by a thick section of marine laminated siltstone and local carbonate deposited in supratidal conditions. Correlation with glacigene sequences in NW Australia suggest an age of 660-680 Ma for the Marinoan Glaciation. The Sturtian Glaciation is post-800 Ma and pre-680 Ma. It presumably falls in the lower (Varangian) part of the Vendian. The Wilpena Group at the top of the Adelaidean contains several units of sandstone, dolomite and quartzite containing the Ediacara fauna at the top in the upper Pound Quartzite. The Wilpena Group occupies the upper (Ediacaran) part of the Vendian (ca. 570-620 Ma). 9.2.2 Western New South Wales A thinner but still thick (ca. 12 km) Adelaidean Sequence can be traced northeastwards from the Flinders Ranges into the Barrier Ranges north of Broken Hill and thence into the Amadeus and Ngalia Basins of central Australia (Thomson, 1969; Preiss et al., 1978). In the Barrier Ranges (Cooper, 1979; Pogson & Scheibner, 1976), the Poolamacca Group at the base containing the Wilangee mafic volcanics is equivalent to the Callanna Beds. The overlying Torrowangee Group contains a lower glacial sequence (Yancowinna Sub-group Sturtian) an interglacial sequence of siltstone, quartzite, sandstone and carbonate (Eurowie Sub-group) and an upper glacial sequence (Teamsters Creek Sub-group Marinoan). The uppermost Farnell Group of siltstone, dolomite and quartzite contains a trace fauna near the top (Lintiss Vale Formation) and correlates with the Wilpena Group of the Flinders Ranges. * 9.2.3 Antarctica Upper Proterozoic sediments were deposited mainly as turbidite fans from the continental margin of the East Antarctic craton, which was downwarped along the present trend of the Transantarctic Mountains. Although not studied in detail, the rocks are broadly correlative on lithology, petrography, greenschist metamorphism and structural style; comprising thick units of quartzofeldspathic metagreywacke, argillite, slate-phyllite with thinner units of quartzitic sandstone and rare limestone and volcanics, deposited on an unknown ?sialic basement. Sparse, poorly-preserved acritarchs are described in some Russian publications (e.g. Iltchenko, 1972) as Vendian or Riphean. Radiometric K-Ar dating of phyllites and slates has generally provided early Palaeozoic ages corresponding to the Ross Orogeny (Adams, Gabites & Grindley, 1982, Adams et al., 1982). At the head of the Ross Ice Shelf, (Fig. 6) the La Gorce Formation of the Queen Maud Mountains (Stump, 1976) has provided a Rb-Sr isochron of 714 ± 27 Ma, and is intruded by late Proterozoic granitoids, Rb-Sr dated at 600 ± 30 Ma (Easton, 1970). The immediately younger Wyatt Formation of silicic porphyry and ignimbrite, is dated at 620 ± 14 Ma (Faure et al., 1968), 620 ± 70 Ma (Ford et al., 1963), 788 ± 14 Ma (Faure et al., 1979). Closer to the Ross Ice Shelf, the Duncan Formation of McGregor (1965) is a more metamorphosed, fault-bounded metagreywacke suite (Stump, 1981). In the central Transantarctic Mountains, the Goldie Formation of the Beardmore Group is a thick (6 km + ) closely folded metagreywacke-phyllite sequence overlying the Cobham Formation of schist, marble and quartzite and unconformably underlying the Early Cambrian Byrd Group (Grindley & Laird, 1969). It is widely intruded by Ordovician post-tectonic granitoids giving K-Ar whole rock ages on slates of 450-500 Ma and a Rb-Sir isochron date of 525 ± 28 Ma (Gunner, 1976) presumably dating an early phase of the Ross Orogeny (Adams Gabites & Grindley, 1982).

Principal correlations and events

In Northern Victoria Land, the Robertson Bay Group is a thick, closely folded, quartzofeldspathic metagreywacke-slate-phyllite sequence that contains Riphean acritarchs east of the mouth of the Rennick Glacier and Vendian acritarchs close to the faulted margin of the Bowers Trough (Cooper et al., 1982). The Berg Group, lying 250 km west of the Rennick Glacier, is a similar metagreywacke- slate-phyllite sequence with thin marble and calc-silicate bands, yielding Riphean acritarchs (Iltchenko, 1972). Simiar metasediments occur at Cape Hunter in Commonwealth Bay, Adelie Coast (Stillwell, 1918), in the Morozumi Range of the Rennick Glacier (Dow & Neall, 1974) and in the Priestley Glacier north of Terra Nova Bay (Skinner & Ricker, 1968). 9.2.4 Tasmania 'Younger' Precambrian basement rocks in Tasmania are composed of comparatively unmetamorphosed sedimentary sequences including orthoquartizte and siltstone (Rocky Cape Group, Oonah Formation), quartz-wacke turbidites (Burnie Formation, Badger Head Block) and siltstone-dolomite- quartzite-quartzose greywacke (Jubilee Block). Some sequences contain Vendian acritarchs (Oonah and Burnie Formations, Smithton Dolomite). The Burnie Formation, Rocky Cape Group and Oonah Formation were all folded in the late Precambrian Penguin Orogeny, dated at 725 Ma by the syn-tectonic Cooee dolerite dikes. Slightly younger Rb-Sr isochron dates (590 ± 40 Ma) are obtained from metamorphic rocks of the Tyennan Nucleus and are thought to date the D3 event of post-metamorphic folding and crenulation cleavage development. Precambrian ages ranging from 715 to 750 Ma were also obtained by RbSr dating of muscovites from syntectonic granite rocks intruding folded Rocky Cape Group correlates, on King Island, together with a rather poor isochron date of 835 ± 60 Ma (McDougall & Leggo, 1965). The Rocky Cape Group is overlain unconformably by the Smithton Dolomite with Vendian acritarchs, followed by a mafic volcanic suite, believed to be early Cambrian. Slates from the folded Burnie and Oonah Formations give K-Ar whole rock dates of 670-690 Ma (Black & Adams, 1980). The Oonah Formation is unconformably followed by the Success Creek Group with Vendian acritarchs, again reflecting the Penguin Orogeny. 9.2.5 New Zealand A quartzofeldspathic sandstone, siltstone and quartz-greywacke suite of a rather uniform composition was metamorphosed in the late Precambrian to produce the Charleston Metamorphic Group which unconformably underlies the Greenland Group in the Paparoa Range south of Westport. The Victoria Paragneiss bears a similar relationship to the lower Paleozoic Waiuta Group in the Victoria Range between Springs Junction and Reef ton. Rb-Sr isochron ages of 670 ± 20 Ma were obtained from the Charleston Metamorphic Group (Adams, 1975) and similar Rb-Sr ages have been obtained from the Victoria Paragneiss (Tulloch, in press). 9.3 Early to Middle Cambrian Volcanics and Ultramafics A striking feature of the correlation chart is the widespread distribution of mafic-intermediate volcanics of Early to Middle Cambrian age. They are present in the Adelaide Geosyncline sequence marginal to the Gawler Craton in South Australia, in the Gnalta Shelf sequence of Western New South Wales, in the trough sequences of Tasmania and Northern Victoria Land and in the Cambrian belts of uncertain tectonic and structural setting in Victoria and New Zealand. In contrast, they are scarce or absent in the Vendian and post-Cambrian sequences of all regions. In trough successions, such as those of the Dundas, Dial Range, Smithton, and Bowers troughs, the volcanics are generally spilitised and locally interbedded with clastic sediments.

Principal correlations and events

Small ultramafic bodies are associated with mafic volcanics in New Zealand, some of the Cambrian belts of Victoria, and the Dundas Trough sequence of Tasmania, and have been faultemplaced into younger Cambrian sediments during the Middle or Late Cambrian interval. 9.3.1 Western New South Wales Pillow basalts and mafic intrusives are associated with Lower Cambrian sediments along the margins of the Wonominta basement block to the east of the Bancannia Trough. The Mount Wright Volcanics were originally interpreted as representing a calc-alkaline island arc sequence by Scheibner (1972, 1976). Detailed geochemical studies have shown that the basalts on the western margin are alkaline whereas those on the eastern margin are tholeiitic (Edwards, 1979). They could, therefore, represent penological variations across an early Cambrian primitive island arc, the inferred subduction zone lying to the east of the Wonominta Block. This interpretation is at variance with the supposed Precambrian age for the Wonominta Complex (Edwards, 1978). 9.3.2 Antarctica Calc-alkaline volcanism commenced in the late Precambrian (Vendian) in the Queen Maud Mountains with eruption of massive silicic porphyries and ignimbrites into the turbidites of the La Gorce Formation of the Beardmore Group. These Wyatt Metavolcanics accompanied the emplacement of a calc-alkaline granitoid batholith along the axis of the Queen Maud Mountains during the Beardmore Orogeny (McGregor, 1965; McGregor & Wade, 1969). In the Early Cambrian, a calc-alkaline volcanic arc became active farther to the northeast. Early basaltic extrusives were succeeded by rhyolitic lavas and pyroclastics associated with volcaniclastics and carbonate banks, (Taylor and Fairweather Formations) and finally by orthoquartzite and limestone, all included in the Liv Group of Stump (1982). Similar calc-alkaline extrusives are present sporadically in the Cambrian Byrd and Skelton Groups in the region between the Nimrod and Koettlitz Glaciers (Skinner, 1965, 1982). In North Victoria Land, volcanics of Middle Cambrian age and dominantly mafic character were erupted in the Bowers Trough mainly as flows, pillow breccias and tuffs, interbedded with marine, volcaniclastic, pelitic and turbiditic sediments (Laird et al., 1982). Preliminary geochemical data suggest calc-alkaline affinities (S.D.Weaver, pers. comm.). Interbedded felsic and intermediate volcanics occur as pebbles in interbedded conglomerate. 9.3.3. Tasmania Two major mafic volcanic associations are recognised in Tasmania (Foden, 1973; Brown et al., 1980). The most widespread are spilitised olivine tholeiites (Motton, Smithton, etc.) chemically similar to recent ocean floor basalts but with close affinities to the Mesozoic tholeiites of Southern Africa and eastern North America that are associated with intra-continental rifting. Some of these volcanics are coeval with Middle Cambrian Dundas Group sediments, but others occur within the Crimson Creek Formation of possibly Early Cambrian age. The mafic volcanics associated with the ultramafic-mafic complexes are distinctly different low-Ti0 quartz tholeiites, and include high-magnesia andesites believed capable of precipitating the ultramafic-mafic cumulates (Rubenach, 1974; Varne & Brown, 1978; Brown et al., 1980). A third but volumetrically minor mafic association comprises altered alkaline basalts occurring in the upper part of the Oonah Formation at Zeehan. These are thought to have heralded the early (late Proterozoic) rifting stage of the Dundas Trough (Foden, 1973; Brown et al., 1980). Although the Tasmanian ultramafic complexes have previously been interpreted as dismembered fragments of oceanic crust (e.g. Rubenach, 1973; Williams, 1978) they might also 2

Principal correlations and events

have formed during the waning stages of igneous activity associated with aborted rifting of continental crust (Brown et al., 1980). The Mount Read calc-alkaline volcanics form an arcuate belt 15-20 km wide around the Tyennan Nucleus at the eastern and northern margins of the Dundas Trough (Fig. 7). A central belt rich in silicic lavas and ash-flows, with relatively minor andesite (about 15%) and very minor basalt, is flanked to the west by submarine sequences of silicic pyroclastics and sediments. A calcalkaline andesite sequence, probably related to the Mount Read Volcanics, occurs within the Dundas Trough sedimentary sequence south of Cape Sorell (White, 1975; Brown et al., 1980). The age of the Mount Read Volcanics remains a problem, but recent stratigraphic and radiometric studies (Corbett, 1979, 1981; Black & Adams, 1980) suggest the majority may be Middle to Late Cambrian (i.e. equivalent to the Dundas Group) and hence younger than many of the basaltic rocks of the Dundas Trough. The Mount Read Volcanics, despite some petrographic and geochemical similarities to Andean-type continental margin volcanic arcs, do not appear to be related to a subduction zone, and indeed it would be difficult to imagine a plate tectonic model that would produce an arc with such extreme curvature and narrow width. Impression of the curved shape by oroclinal bending related to transcurrent movement on the Tamar Line as suggested by Crawford & Campbell (1973) has been rejected by other workers (Daily et al., 1973; Harrington et al., 1973). The apparent scarcity of andesites and basalts is also a problem for subduction models and is a significant difference from other volcanic suites in the region, with the possible exception of the poorly exposed Stavely Belt of Western Victoria. Melting of continental crust by residual heat from rising mantle associated with emplacement of the ultramafic bodies in the Dundas Trough has been suggested as a possible origin for the Mount Read Volcanics (Brown et at., 1980).

9.3.4 Victoria The Greenstone Axial Belts of Victoria have received a variety of plate tectonic interpretations, generally based on minimal geochemical evidence. The most modern geochemical and petrological study by Crawford & Keays (1978) has shown that the northern and southern portions of the Heathcote Belt and the Mount Wellington Belt are composed of mafic lavas and intrusive mafic to ultramafic sheets that resemble dismembered ophiolite suites (see also Crook & Felton, 1975). The Waratah Bay Belt is similar to the Mount Wellington Belt although lacking an ultramafic component apart from a small diapiric intrusion of serpentinised gabbro-pyroxenite. Subaerial hornblende andesites with well developed columnar jointing are exposed on the Barkly River Belt and meta-andesites with associated pyroclastics are also present in the central sector of the Heathcote Belt. The Mount Staveley Belt is dominantly a calc-alkaline intermediate felsic volcanic arc suite ranging from hornblende andesite to dacite. Crawford & Keays (1978) favour the possibility of the central Heathcote calc-alkaline segment and the Mount Stavely Belt being rifted segments of a single arc. Presumably the Barkly River Belt, not mentioned by Crawford & Keays (1978), would be interpreted similarly. However, it is by no means certain that the Bendigo and Melbourne troughs are underlain by oceanic crust as demanded by their hypothesis. Geochemical evidence indicates that the Heathcote and Mount Wellington metabasalts and dolerites are low K 2 0 tholeiites that on trace element data fall into the field of ocean ridge basalts erupted from spreading centres. Aeromagnetic evidence indicates that the Mount Wellington and Heathcote Belts join to the north near the New South Wales border whereas the Mount Stavely Belt continues for at least 300 km to the northwest below the Murray Basin (Fig. 8).

Principal correlations and events

9.3.5 New Zealand The Devil River Volcanics are a dominantly intermediate-mafic calc-alkaline volcanic arc suite. The basal volcanics resting conformably on continent-derived arkoses and pelites of the Balloon Formation are metadacites and rhyolites fed by quartz porphyry dykes. Further rifting of the continental crust led to the eruption of more mafic low K andesites and basalts. Preliminary geochemical work indicates variation from aphyric spilitic basalts to porphyritic plagioclase and pyroxene andesites typical of a calc-alkaline island-arc suite. The younger Cambrian intrusives frequently contain phenocrysts of augite and show mildly alkaline affinities (Hunter, 1977). The ultramafic-mafic Cobb Igneous Complex has been interpreted as an ophiolitic slab, exposed by rifting of continental crust and later emplaced upward during the mid Cambrian compressive phase (Grindley, 1980) or as a slice of a stratiform intrusion (Hunter, 1977). A close similarity with the Tasmanian ophiolitic complexes is apparent, in both field relations and timing of emplacement.

9.4 Middle Cambrian - Early Ordovician Tectonic, Intrusive, Metamorphic and related sedimentary events A major orogenic cycle in the Late Cambrian and Early Ordovician is reflected by events in the history of each region. 9.4.1 South Australia The Kangarooian movements terminated sedimentation in the Kanmantoo Trough on Kangaroo Island and the Mount Lofty Ranges in the Middle Cambrian (Daily & Milnes, 1973). Farther north in the Flinders Ranges, sedimentation continued without interruption, but was terminated in the late Cambrian by the influx of coarse clastics from the Delamerian Fold Belt. The Kanmantoo Trough and adjoining Adelaidean sequence were strongly deformed in the Late Cambrian. Polyphase deformation and high T/low P regional metamorphism (Offler & Fleming, 1968) were preceded by the prekinematic Encounter Bay granites, Rb-Sr dated at 496-506 Ma (Milnes et al., 1977). Folding, regional metamorphism and uplift continued for a further 50 Ma as shown by K-Ar dating. Post-kinematic granites, rhyolites and quartz porphyries were emplaced, following the Delamerian Orogeny, along the Padthaway Ridge (Webb, 1976) presumably into Kanmantoo country rocks. Further southeast in western Victoria, deformation and regional metamorphism of the Glenelg River Beds in the Late Cambrian (512 ± 9 Ma, K-Ar dating) followed emplacement of mafic and ultramafic intrusives in the Middle or Early Cambrian, and preceded emplacement of the Wando Granodiorite and Dergholm Granite in the Early Ordovician (460-490 Ma: Bowen, 1975). Contemporaneously with, and immediately following these tectonic movements, a flood of quartz-rich detritus spread throughout all regions. Coarse, near-source, quartz-rich conglomerate and sandstones are present in the Bynguano and Scopes Range of Gnalta, Flinders Ranges, Northern Victoria Land (Leap Year Group), and Tasmania (Owen Formation and Denison Subgroup) implying nearby mountainous regions. More distal deposits are probably represented by . the thick quartz-rich, poorly sorted sandstones in turbidites sequences of latest Cambrian or Early Ordovician age in Victoria (Bendigo Sedimentary Belt) and New Zealand (Western Sedimentary Belt) implying an extensive and rapidly rising source area. The continued accumulation of thick sequence of quartz-rich, clastic trough sediments in Victoria and New Zealand through the Early and Middle Ordovician implies continued uplift and erosion in the source area, consistent with the evidence from South Australia mentioned above.

Principal correlations and events

9.4.2 Antarctica In the central Transantarctic Mountains, limestone deposition ceased probably by the end of the Middle Cambrian and coarse clastic sedimentation followed in restricted basins, accompanied by sporadic andesitic and rhyolitic volcanism. However, the major volcanic arc activity during the Cambrian lay farther south where calc-alkaline rhyolites, silicic pyroclastic and associated volcaniclastics, quartzites and carbonates characterised the Early and Middle Cambrian of the Queen Maud Mountains (Liv Group of Stump, in press). A similar volcanic arc sequence is also present further southeast in the Wisconsin Range where rhyolite is dated at 488 ± 45 Ma (Faure et al., 1968) and interbedded limestones (Leverett Formation) contain Middle Cambrian trilobites (Palmer & Gatehouse, 1972). Further north in the McMurdo Sound region, the Anthill Limestone (Gunn & Warren, 1962) of presumed Cambrian age is overlain unconformably by coarse conglomerate containing clasts of andesite, porphyrite, granite and marble with interbedded volcaniclastic sandstone and minor pillow lava (Skinner, in press). The metamorphic grade rises northwards to amphibolite facies and a complex polyphase deformational history associated with pre-kinematic and syn-kinematic granitoids is postulated (Smithson et al., 1970; Williams, et al., 1971; D.N.Skinner & R.H.Findlay, in prep.). Orogenic activity may have lasted to the end of the Cambrian and was followed by early Ordovician post-kinematic granites dated at 460-490 Ma (Faure & Jones, 1974; McDougall & Ghent, 1970). The Bowers trough of northern Victoria Land, was uplifted following the Vendian-Early Cambrian sedimentation and mafic volcanism of the Sledgers Group. No major folding or metamorphic event is, however, recorded prior to deposition of the overlying Mariner Group of late Middle - Upper Cambrian age. The deposition of coarse clastics (Leap Year Group) followed in the latest Cambrian and early Ordovician reflecting orogenic uplift along the trough margins and deformation of the Precambrian Wilson and Robertson Bay Groups (K-Ar ages - 460-500 Ma). Ordovician granitoids are restricted to the western block and extended a long way west across the Precambrian craton. The trilobite faunas of the Transantarctic Mountains, are dominated by non-agnostids, (Clarkson et al., 1979) a feature attributed by Palmer & Gatehouse (1972) to sedimentation in restricted basins, formed probably by the rise of orogenic ridges barring access to the open sea, in the early phases of the Ross Orogeny. 9.4.3 Tasmania Following early Cambrian rifting and mafic volcanism, the Dundas trough appears to have been disrupted sufficiently to cause fault emplacement of the ultramafic bodies into the sedimentary sequences, where they were eroded into middle Middle Cambrian sediments of the Dundas Group. A more pronounced compressional phase appears to have affected the Adamsfield Trough at about the end of the Middle Cambrian, producing a widespread unconformity and an ultramafic diapir that was subsequently eroded into the Late Cambrian sediments of the Denison Subgroup. Intrusion of sub-volcanic granite bodies occurred within the Mount Read Volcanics probably at this time, and sections of the volcanics and granite were uplifted and eroded, shedding detritus into the Tyndall Group and correlates in the late Middle and early Late Cambrian. A large influx of coarse siliceous detritus from the uplifted Tyennan Nucleus blanketed the Mount Read volcanic belt in the later part of the Late Cambrian, when up to several kilometres of Owen Conglomerate and correlates was deposited in fault-controlled grabens bordering the nucleus. The conglomerate sequence, which includes a basal quartzose flysch facies at the Tyndall Range (Newton Creek Sandstone Member), overlapped the Tyndall Group conformably in some areas and unconformably in others. The Haulage Unconformity in the upper part of the

Principal correlations and events

Owen Formation indicates that local movements continued into the Early Ordovician. K-Ar whole rock ages of 470-490 Ma on slates within the Mount Read Volcanics may also reflect early Ordovician uplift (Black & C.J.Adams, 1980). 9.4.4. Victoria Cambrian tectonic activity is confined to the Greenstone belts except in areas of western Victoria affected by the Delamerian Orogeny. Sediments close to the Stavely Belt contain volcaniclastics and tuff suggesting intermittent subaerial volcanism. Similarly, the central section of the Heathcote Belt consists of meta-andesite and tuff, pebbles of which are present as derived clasts in the Middle Cambrian Knowsley East Formation and Monegeeta Shale. The Mount Wellington Belt consists of metabasalt, volcaniclastics and cheft intruded by dolerite, gabbro and ultramafics all metamorphosed to the greenschist or prehnite-pumpellyite facies. Meta-andesite occurs in the adjoining Barkly river Belt (cf. Heathcote). Metamorphism and uplift of the belt took place in the Middle Cambrian allowing erosion of serpentinised ultramafics and metasomatised volcanics into the unconformably overlying Garvey Gully Formation of late Middle Cambrian age. At Waratah Bay, a similar mafic volcanic sequence is faulted against Tremadocian limestone, and diapirically intruded by serpentinised gabbro and pyroxenite. 9.4.5 New Zealand The Central Belt Volcanics were uplifted by block-faulting in the late Middle Cambrian and intruded by a thick slab of sub-volcanic ultramafic and mafic cumulates, emplaced through a dynamically metamorphosed greenschist envelope (Grindley, 1980). Coarse conglomerates (Lockett Conglomerate) were deposited on the flanks of the volcanic belt and across older Cambrian formations uplifted in fault blocks, and contain detritus from all the older Cambrian formations including the ultramafics. Thick chert-volcaniclastic flysch followed in the Late Cambrian. In contrast to all other regions, except Eastern Victoria, the Late Cambrian - Early Ordovician orogenic movements did not reach the New Zealand Central and Eastern Belts, where predominantly carbonate shale and quartzite deposition indicates a period of relative tectonic calm.

9.5 Ordovician clastic sedimentation 9.5.1 Western Tasmania Lower Ordovician conglomerate and quartz sandstone deposits are followed by a change to mudstone, then carbonate (Gordon Subgroup), deposition, indicating relatively shallow marine deposition under tectonically stable conditions throughout late Early, Middle, and most of Late Ordovician time. 9.5.2 Victoria and Northeast

Tasmania

The Ordovician is represented by deposition of predominantly quartz-rich turbidite sandstone, mudstone and black shale in the Bendigo and Melbourne Trough belts. The Upper Ordovician Riddell Grits were deposited along the western margin of the rapidly sinking Melbourne Trough and indicate a rising source area to the west. Part of that source area may have been formed by the western part of the Bendigo Trough and by the Stawell Sedimentary Belt. To the east, in the Mount Easton Province, Middle and Late Ordovician time is represented by a relatively condensed black shale. Further to the east, in Eastern Victoria, Early, Middle and Late

Principal correlations and events

Ordovician time is represented by a thick, poorly fossiliferous turbidite sandstone and mudstone sequence, deposits of a distinct, but mainly metamorphosed sedimentary trough (Wagga Trough). In northeast Tasmania, the Mathinna Beds are a thick sequence of phyllitic and turbiditic sediments, contrasting markedly with the carbonate sequences west of the Tamar Contact Zone. 9.5.3 New

Zealand

As in Tasmania and Victoria, two contrasting sedimentary successions are also present in the New Zealand Ordovician, those of the Western and Eastern Sedimentary Belts. The Western Sedimentary Belt contains a trough sequence of quartz-rich turbidite sandstone, mudstone, quartzite and black shale similar to that of the Bendigo Sedimentary Belt (Cooper, 1975). The Eastern Belt is comprised largely of a carbonate-shale complex but does include quartz-rich sandstone in the Upper Ordovician. Unlike the comparable sedimentary facies of Victoria and Tasmania the two Ordovician successions in New Zealand have been mapped as grading into each other around the northern end of what is interpreted as an allochthonous Central Belt by Bishop (1971) and Grindley (1971), and are thus thought to be not separated by a major tectonic boundary as in NE Tasmania (Tamar Contact Zone, see 9.9).

9.6 Late Ordovician - Early Silurian tectonic, metamorphic,

igneous and sedimentary

events

The Benambran Orogeny in the Early Silurian of Eastern Victoria produced polyphase deformation, amphibolite facies metamorphism, syntectonic granite intrusion, migmatisation and uplift of the Ordovician (Hotham Beds) of the Wagga Trough which then formed a basement for subsequent sedimentation. The earliest folding of the Bendigo Sedimentary Belt and of the Western Belt (of New Zealand) may have taken place at this time, but elsewhere an equivalent tectonic event is not indicated, except by concentrations of K-Ar whole rock ages on slates in many areas. A marked change in sedimentary facies and style, however, occurred widely across Tasmania, Victoria and New Zealand in the late Ordovician or basal Silurian. In Western Tasmania and the Eastern Belt of New Zealand, carbonate or carbonate-shale deposition in the Ordovician gave way to shallow marine quartz-sandstone deposition with relatively minor siltstone, through the entire Silurian. In the Melbourne Trough, Ordovician black shale gives way to Silurian siltstone and turbiditic clastics, rapidly deposited in the western part (Darraweit Guim Province) but relatively condensed farther east (Moutn Easton Province). In Eastern Victoria, the sedimentary style changes from broad-scale turbidite deposition in a large trough (Wagga Trough), as represented by the Hotham Beds, to locally derived shallow marine clastics, limestone and volcanics filling small troughs and fault-angle depressions. In Western Victoria an extensive depression (Grampians Trough) was formed in the basement of folded and indurated sediments and volcanics of inferred Cambrian age, and filled with a thick, largely non-marine, sequence of quartzose sandstone, siltstone, and mudstone, during the Middle to Late Silurian. In summary, the latest Ordovician to earliest Silurian marks a period of rapid change in sedimentary style throughout the regions under study, an interval of intense deformation and metamorphism locally, and regional uplift elsewhere leading to closure of K-Ar isotopic systems.

9.7 Late Silurian to Early Devonian

tectonic, metamorphic,

igneous and sedimentary

events

In the Early Devonian, Ordovician and Silurian rocks of the Benambra Sedimentary Belt were deformed in the Bowning Orogeny, an event which can be traced widely throughout the Lachlan

Principal correlations and events

Fold Belt in New South Wales (Packham, 1969; Gilligan & Scheibner, 1978). Generally moderate folding was accompanied by minor granite emplacement, but in Eastern Victoria the deformation was more intense and was accompanied by low grade metamorphism (Table 2). Mild folding of the Silurian to lowest Devonian Grampians Group in Western Victoria preceded emplacement of Lower Devonian granite and is ascribed to the Bowning Orogeny. Lower Devonian granites were also emplaced in the Stawell Sedimentary Belt (K-Ar ages 395410 Ma). A number of metamorphic or folding events took place widely throughout the regions studied at about the time of the Bowning Orogeny. In Northern Victoria Land, K-Ar whole rock dates on Sledgers and Mariner Group rocks suggest rapid uplift and cooling in the Late Silurian and Early Devonian (380-420 Ma) after a metamorphic event (Adams et al., in press) accompanying strong folding of the Bowers Supergroup in the Borchgrevink Orogeny. Similarly, K-Ar and Rb-Sr data in the Mount Lofty Ranges of South Australia suggest a metamorphic event in the latest Silurian and Early Devonian (Milnes et al., 1977). In New Zealand, the Eastern Sedimentary Belt sequence was recumbently folded and metamorphosed and the Central Belt emplaced over the Eastern and Western Belts by recumbent folding and thrusting in the latest Silurian to Early Devonian (F1 phase of the Tuhuan Orogeny, Grindley, 1978b). The Early Devonian marks a widespread change in sedimentary facies. In Western Tasmania, the Western Melbourne Trough and Eastern Belt of New Zealand, Silurian quartz-rich sandstones gave way to dominantly mudstone deposition with minor limestone. The Walhalla Group (5000 + m thick) in the Eastern Melbourne Trough and Baton Formation (2600 m thick) of the Eastern Belt of New Zealand indicate rapid sinking and filling of localised depositional basins in the late Early Devonian, as do the Wentworth Group (1000 m) and Buchan Rift (with 34000 m of Snowy River Volcanics and 1000 m of Buchan Group) in Eastern Victoria.

9.8 Middle-Late

Devonian

tectonic, metamorphic and igneous events

At the end of Early Devonian time, marine deposition ceased in Victoria, Tasmania and New Zealand. A major orogeny took place in the Middle or (in New Zealand) Middle to Late Devonian. Two phases of deformation are widespread in Central and Eastern Victoria separated by intermediate-mafic dyke swarms and some granites (Table 2). Block-faulting, felsic volcanism and intrusions of sub-volcanic plutons followed in the late Devonian. A regionally developed penetrative cleavage and low grade (up to Greenschist Facies) metamorphism accompanied a single phase of folding (F2 phase of the Tuhua Orogeny) in New Zealand. In Western Tasmania at least two phases of folding are present (Williams 1978) with widespread development of penetrative cleavage. K-Ar dates of 400-430 Ma appear to record the main folding and regional metamorphism in this area (Black & Adams, 1980; C.J.Adams, pers. comm.). In northeastern Tasmania a main phase of regional strong folding and associated penetrative cleavage affected the Mathinna Beds, with crenulation by a later cleavage in some areas (Williams, 1978). Rb-Sr dates of 400-425 Ma on the Mathinna Beds are thought to record the main folding (Cocker, 1977). A regional and clearly defined unconformity was produced in all three regions. Widespread emplacement of post-kinematic granitoids followed, in Victoria, Tasmania, Northern Victoria Land and New Zealand. In the eastern Bendigo Trough, and western Melbourne Trough, latest Devonian to Early Carboniferous K-Ar ages (360-380 Ma) on granites probably represent uplift and cooling following emplacement. In western Tasmania, minimum ages (Rb-Sr, K-Ar) are mostly in the range 342-369 Ma (Late Devonian to Early Carboniferous) whereas in Northeastern Tasmania ages (Rb-Sr, K-Ar) are mainly in the range 350-395 Ma (Middle Devonian to Early Carboniferous). Concordant mineral and whole rock Rb-Sr ages of 350-365 Ma (Aronson 1968) of Tuhuan granites in New Zealand suggest emplacement in latest

Principal correlations and events

Devonian or early Carboniferous. In Fiordland, a late Devonian Rb-Sr whole rock isochron (372 Ma) has been derived by G.J.H.Oliver (Oliver & Coggon, 1979) on the Deas Cove Granite. The Admiralty Intrusives, emplaced within the Robertson Bay Group in Northern Victoria Land, have given K-Ar whole rock ages of 360-395 Ma (Gair et al., 1969), suggesting emplacement from Middle Devonian to Early Carboniferous time. The Tabberabberan-Tuhuan event was a terminal orogeny, in the sense that it brought to an end a long history of localised tectonism and subsidence with rapid filling of marine troughs and basins, and uplift and erosion of intervening blocks. All regions became technically stable, and effectively cratonised, behaving thereafter more as a rigid platform than as part of a mobile belt. There may, however, have been some transcurrent displacement on the Tamar Contact Zone during or immediately following the emplacement of the granites, to bring the contrasting parts of Tasmania together. A new and completely different style of sedimentation ensued widely throughout Southeast Australia and the Transantarctic Mountains, characterised by continental quartz sandstone deposition.

9.9 Bass Strait structures, palaeomagnetics, 9.9.1 Geological and geophysical

and Tasmania

- Victoria relationships

data

The apparent lack of correlation between western Tasmania and Victoria is difficult to resolve because of the scarcity of information on the basement geology of Bass Strait. Several authors have suggested major transcurrent dislocations between the two areas in the Palaeozoic, prior to the Mesozoic break-up (e.g. Harrington et al., 1973). For the most part, the basement is buried by the deep Cretaceous-Tertiary sequence of the Bass Basin (Fig. 5), which reaches a thickness of at least 3600 m in the central part of the Strait (Brown, 1976; Ellenor, 1976; Douglas & Ferguson, 1976; Griffiths, 1971; Richards & Hopkins, 1969). The eastern edge of the basin is a basement ridge (Bassian Rise) showing outcrops of Devonian granite, and there appears to be a continuity between Flinders Island (which contains Mathinna Beds sediments) and Wilsons Promontory. The narrow Cambrian greenstone belt at Waratah Bay is flanked by the Lower Devonian Liptrap Formation (proximal flysch or shelf) which in turn is flanked by Late Ordovician - Silurian graptolitic sequences. Aeromagnetic anomalies suggest that the greenstone belt, which includes gabbro and serpentinite, extends at least 30 km into Bass Strait, and possibly swings into a southerly trend (Beattie, 1978). To the west, a buried basement ridge extends northwards from King Island towards the Mornington Peninsula, in the area where the Bass Basin connects with the Torquay Embayment (an easterly extension of the Otway Basin). The continuation of this ridge on Mornington Peninsula consists of Lower Ordovician graptolitic flysch with some Middle and Upper Ordovician and Silurian of similar facies. The rocks are intruded by Upper Devonian granites, and are clearly more akin to the Mathinna Beds than to the Palaeozoic sequences of western Tasmania. The prominent magnetic high extending south from the peninsula is related to Tertiary basalt (Hematite Expl., 1965). The nature of the southern part of this buried ridge is not known, although towards King Island the trends suggest continuity with the Precambrian - Palaeozoic basement of that area. A prominent magnetic high off the east coast of the island probably reflects an extension of the Cambrian spilites. Magnetic trends off the north west coast of Tasmania suggest continuity of NE-oriented basement structures, including the Arthur Lineament, for possibly 50 km. These trends are interrupted by the strong NW-oriented trends of the Bass Basin, which are mainly related to basin-forming faults. Some fault-angle depressions in the basin are estimated to contain up to 3000 m of Lower Cretaceous sediments (Brown, 1976).

Principal correlations and events

Continuity of western Tasmania basement at least as far north as the Bass 3 drill hole is indicated by core from that hole, which was drilled on a basement high near the south-west basin margin (Esso Expl., 1967). The hole penetrated some 2350 m of Cainozoic (and possibly Late Cretaceous) sediments, and some 43 m of basement. Examination of the basement core held at the Tasmanian Mines Department shows it to consist of black chert, recrystallised chert, chert breccia, hard black shale and dolomitic shale. The rocks are remarkably similar to the chert-shale sequences which form a large proportion of the Smithton Dolomite in the Smithton Trough, some 100 km south of the drill hole. Correlation might also be possible with chert-shale units in the (?)Cambrian sequence on the western side of the Badger Head block near Beaconsfield (Gee & Legge, 1974), but there is no similarity with the Mathinna Beds. A K-Ar age determination on the core gave a Silurian date, but this is likely to be a minimum age only. The Bass 2 drill hole, located on another structural high near the eastern margin of the basin (Fig. 7), is also purported to have reached basement at 1653 m (Esso Expl., 1966). The core (1653-1773 m) consisted of altered basic to intermediate volcanic rock underlain by tuffaceous mudstone, and was initially thought to be Mesozoic. An Early Cretaceous radiometric date (KAr) was obtained from the volcanic rock, but was considered unreliable, whereas the mudstone gave an Early Cambrian - Late Precambrian date (Brown, 1976). Examination of the core shows the volcanic rock to be very weathered, oxidised and altered to clay minerals, with original texture almost completely destroyed. The laminated tuffaceous mudstone is horizontally bedded, uncleaved, and contains veins of white clay. It does not resemble any known Palaeozoic or Precambrian rocks in Tasmania, and the lack of cleavage, the relatively weak induration, and the presence of unmetamorphosed clay material, strongly suggests that it is post-Devonian. The only other hole known to have reached basement is Clam 1, located some 40 km west of the coast near Smithton (Fig. 5). This hole bottomed in vertically-dipping metasiltstone similar to the Rocky Cape Group (Gee, in Lunt, 1970), above which was some 47 m of less indurated grey siltstone of possible early Palaeozoic age. An unusual 'red-bed' sequence of conglomerate and siltstone (187 m), possibly of Late Devonian or Mesozoic age, occurred between the grey siltstone below and the 1280 m section of Late Cretaceous and Cainozoic above. 9.9.2 Palaeomagnetic

data

The few palaeomagnetic determinations which have been made on Lower Palaeozoic rocks in Tasmania have been variously used in discussions of possible displacements of Tasmania in the Palaeozoic. The original determinations, on rocks which included Middle to Upper Cambrian sediments and tuffs, and a syenite intrusion (possibly Ordovician?), in the Dial Range Trough, were by Briden (1967). He considered the remanant magnetism to be due mainly to Tertiary reheating. McElhinny & Embleton (1974) did not consider the results reliable enough to plot. However, Embleton & Giddings (1974) and Giddings & Emblteton (1974) reworked the samples and plotted a Late Cambrian position at 23°S, 13°E. Since this lay near the apparent polar wander curve for the early Palaeozoic of the Australian platform, they concluded that it was not necessry to invoke local rotation or translation of the Tasmanian region with respect to the platform, and used this as an argument against the rotation-translation model proposed by Crawford & Campbell (1973). They admitted, however, that a relatively simple linear displacement of a few hundred kilometres would probably not be resolved palaeomagnetically. Burns & Embleton (1976) argued that since the Tasmanian pole lay close to the Australia platform polar path as opposed to that of the Lachlan fold belt (the latter based only on Silurian and Devonian results), then western Tasmania had to be considered part of the platform rather than part of the Lachlan orogen since the Cambrian. Any rotations due to rigid motions or structural deformation which affected the orogenic belt should not, therefore have affected Tasmania.

Principal correlations and events

Examination of the data suggests that such generalisations may not be warranted. The pole position, which appears to be based on a diverse sample of tuffs and intrusives, not necessarily all of the same age and some with opposite polarity, has a 95%-confidence circle of radius 11.5°. This allows for lateral displacements of many hundreds of kilometres, and at least some rotation. In addition, the polar wander path is based on a limited number of samples and is by no means well defined. 9.9.3 Conclusions 1. The presence of Mathinna-type sediments on Mornington Peninsula and of western Tasmanian-type basement at Bass 3, suggests that a continuation of the Tamar Contact Zone lies between these two points. A similar change must occur between King Island and Mornington Peninsula. 2. The structural and sedimentary discordance between eastern and western Tasmania suggests at least some transcurrent movement between the two after the main Tabberabberan folding. If movement on the Tamar Contact Zone is related to the granite foliations in the northeast, then the movement is likely to have been sinistral. 3. There appears to be insufficient geological or palaeomagnetic evidence to discount the possibility of western Tasmania having been translated a considerable distance with respect to Victoria, although the timing of any major movement presents a problem.

Problems and recommendations

10 PALAEOTECTONIC/PALAEOGEOGRAPHIC RECONSTRUCTIONS 10.1 Problems in inter-continental reconstructions As stated earlier, it is not the purpose of this paper to speculate on possible Early Palaeozoic reconstructions. In the foregoing text, many correlative features and events have been outlined that are consistent with the regions of this study having together formed a segment of the Late Proterozoic - Early Palaeozoic Gondwanaland super-continent. Listed below, however, are points that are not easily explained in terms of the Late Mesozoic plate tectonic reconstruction of the region (Fig. 1) but which, in our view, must be taken into account in any Late Proterozoic Early Palaeozoic palaeotectonic or palaeogeographic model. 1. The paucity of convincing examples of geological links such as distinctive rock or structural belts that span the present continental boundaries and provide tie points for locating the continental fragments in Palaeozoic reconstructions. 2. The absence of the thick Adelaidean-Cambrian sequence of South Australian from the opposed coast of Antarctica (Adelie Coast) where only older Precambrian basement rocks are exposed. 3. The apparent similarity between regions not juxtaposed in the late Mesozoic reconstruction; for example, the late Proterozoic (Adelaidean) sequences of South Australia and Tasmania, and the Ordovician sequences of the Bendigo Sedimentary Belt and Western Sedimentary Belt of New Zealand. 4. The marked lack of correlation and the contrast in sedimentary facies and tectonic setting between the Cambrian and Ordovician sequences and structures of Victoria and western Tasmania, and between western Tasmania and eastern Tasmania; the significance of the Tamar Contact Zone. 5. The apparent lack of an equivalent of the Robertson Bay Group in Tasmania or SE Australia. 6. The apparent lack of an equivalent of the Mount Read Volcanic Belt in Antarctica, or in southeast Australia. 7. The distinctive structural style (nappes and recumbent folds) developed in the Central Sedimentary Belt of New Zealand as compared with other Cambrian volcanic-sedimetary belts. 10.2 Recommendations for further study 1. Better age control is needed on pre-Middle Cambrian units in Victoria, Tasmania, New Zealand and Antarctica. The work done for this project on acritarchs shows this group to offer a promising avenue for improved age control, but isotopic dating is also needed (such as the recent studies by Adams, Gabites and others on K-Ar dating; Raheim & Compston, on Rb-Sr dating; Gleadow & Lovering on fission-track dating). 2. Sedimentological study and age data are needed on some large and little-known sedimentary terrains such as the Robertson Bay Group of Antarctica, Mathinna Beds and some of the Cambrian sequences of Tasmania, and the St Arnaud and Glenelg beds of Western Victoria. 3. Basin analysis studies of sedimentary belts, particularly those of Victoria and New Zeland, are needed. 4. Further geochemical and structural study of all volcanic and ultramafic belts in the region are needed to elucidate their tectonic setting. 5. Study of basement structure of the Bass Strait region. The almost total lack of information on basement structure and composition beneath Bass Strait is a major obstacle in relating the sedimentary and structural belts of Victoria to those of Tasmania, (see 9.9).

Problems and recommendations

6. Before any geologically reasonable reconstruction of the region in the early Paleozoic interval can be attempted, it will be necessary to undertake detailed structural studies of the folded terranes in North Victoria Land, Victoria, Tasmania and New Zealand to determine crustal shortening, significance of major shear-zones, overthrusts, and sutures, their relationship to the so-called greenstone belts and to the zones of granitic emplacement and metamorphism. 7. Palaeomagnetic studies of mafic and acidic volcanic complexes and associated sediments, especially in North Victoria Land, Victoria and Tasmania, are recommended.

Appendix—South Australia

APPENDIX - NOTES ON CORRELATION CHART SOUTH AUSTRALIA

Middle Cambrian, Yorke Peninsula My Yuruga Formation Mcb Coobowie Limestone Mm Moonan Formation Ms Stansbury Limestone Mc Corrodgery Formation Mr Ramsay Limestone Lower Cambrian, Yorke Peninsula Lm Minlaton Formation Lp Parara Limestone Lk Kulpara Formation Lw Winulta Formation Lower Cambrian, Kangaroo Island Tb Boxing Bay Formation Te Emu Bay Shale Tw White Point Conglomerate Tsb Smith Bay Shale Ts Stokes Bay Sandstone Kc Carrickalinga Head Formation Precambrian Am Marino Group As Sturt Group At Torrens Group Bgn Basement gneiss (part of Barossa Complex) Mount Lofty Ranges, Kangaroo Island Cambrian - Mount Lofty Ranges Kg Kanmantoo Group. Comprises eight formations in three subgroups. In upward sequence they are: Carrickalinga Head Formation, Inman Hills Subgroup (Backstairs Passage Formation, Talisker Calc-siltstone, Tapanappa Formation) Brown Hills Subgroup (Tunkalilla Formation, Balquhidder Formation), Wattaberri Subgroup (Petrel Cove Formation, Middleton Sandstone). Ng Normanville Group. Comprises five formations. In upward sequence, they are: (1) Mount Terrible Formation, which includes a phosphatic shale containing molluscs, conodonts, sponge spicules, and shells of unknown affinity, indicating a Tommotian age (Daily 1976a & b), and the acritarch Bavlinella faveolata; (2) Wangkonda Formation; (3) Sellick Hill Formation; (4) Fork Tree Limestone; (5) Heatherdale Shale. The Truro Volcanics (Tr) occur in the Normanville Group northeast of Adelaide. Middle - Upper? Cambrian, Flinders Ranges Lfg Lake Frome Group Grs Grindstone Range Sandstone Pf Pantapinna Formation Bf Balcoranana Formation Mf Moodlatana Formation W1 Wirrealpa Limestone Lower Cambrian, Flinders Ranges Bcf Billy Creek Formation Hg Hawker Group

Appendix—Western New South Wales

A1 Ajax Limestone Pf Parachilna Formation Ur Uratanna Formation Precambrian, Flinders Ranges Wg Wilpena Group (including Pound Quartzite, Wonoka, Bunyeroo and Brachina Formations, ABC Range Quartzite) Ug Umberatana Group (including Marinoan and Sturtian Glacials and interglacial Tapley Hill Formation and unnamed limestone) Bg Burra Group (many mainly unnamed quartzite, siltstone, dolomite and greywacke units) Cb Callanna Beds (including Wooltana Volcanics correlated with the Beda Volcanics dated at 1076 ± 34 Ma by Mason et al., (1978) and Thomson (1980). Tectonic, Igneous and Metamorphic Events 1. Known time span of Kangarooian Movements (Daily & Milnes, 1973; equivalent to the Cassinian Uplift and Waitpingian Subsidence of Thompson, 1969,1970; see Daily & Milnes, 1971, p.209 for discussion). 2. Gneisses of the Barossa Complex are strongly retrogressed and give a Rb-Sr metamorphic age of c.850 Ma. The significance of this figure is not known. 3. Sturtian uplift and erosion. 4. Duttonian uplift and erosion. 5. Delamerian folding and uplift. 6. Delamerian granites - 6a, Encounter Bay Granites, 504 ± 8 Ma, 495 ± 6 Ma (Milnes et al., 1977). 6b, Palmer Granite, 504 ± 33 Ma, 479 ± 15 Ma (Milnes et al., 1977). 7. Late Silurian - Early Devonian thermal event, inferred on basis of K-Ar ages on biotites from Victor Harbor and Padthaway Ridge (Webb, 1976; Milnes et al., 1977). (Bgn)

WESTERN NEW SOUTH WALES

Gnalta Sequence Cb Cootawundy Beds (Pogson & Scheibner, 1971); contains plant fragments and trilobite tracks. Bs Bynguano Range sequence; comprises Nootumbulla Sandstone with Payntonian to earliest Datsonian trilobites (Shergold, 1971), overlain by Bynguano Quartzite with Warendian trilobites, Rusophycus and Skolithus overlain by Rowena Formation with basal to mid Arenigian trilobites (Shergold, 1971; Jones, Shergold & Druce, 1971). Ss Scopes Range Beds; with Rusophycus, Skolithos, Arthrophycus, equated with Bynguano Range sequence. Cf Coonigan Formation with Ordian - Templetonian faunas (Opik, 1967, 1970; Jell,P.A., 1975; Jell & Jell, 1976; Runnegar & Jell, 1976). Kt Kandie Tank Limestone (Pogson & Scheibner, 1971). Cmr Cymbric Vale Formation, with late Early Cambrian trilobites and archeocyathids (Opik, 1967; Kruse, 1978). Wv Mount Wright Volcanics, with Early Cambrian archeocyathids (Scheibner, 1972); thought by Webby not to extend down into the Vendian because of the lack of volcanic-derived detritus in the upper Torrowangee Group of Broken Hill Block, to the west. Wb Wonominta Beds, possibly equivalent to Callanna Beds (basal Adelaidean). Ev Basic intrusives along eastern margin of Wonominta Block, possibly penological variants of Mount Wright Volcanics (Edwards, 1978).

Appendix—Antarctica

Barrier Range Sequence Ad Acacia Downs Beds (Rose, 1968) Fg Farnell Group (Cooper & Tuckwell, 1971) Tg Torrowangee Group (sensu Rose, 1968, 1970; Cooper, 1975) Tg Torrowangee Group (sensu Cooper & Tuckwell, 1971) Pg Poolamacca Group (Cooper & Tuckwell, 1971) Wc Willyama Complex (see Note 1) Tectonic and metamorphic events 1. The original rocks of the Willyama Complex are estimated to have an Early Proterozoic (± 1800 Ma) age (Thomson, 1975). Tuckwell (1978, p.299) has referred to the youngest part of the Willyama Complex (the carbonaceous Bijerkerno Beds) as having a 'Carpentarian' (1800-1400 Ma) age. Presumably this implies deposition prior to the 1700-1650 Ma age of metamorphism of the Willyama rocks (Cooper et al., 1978, p.50). 2. No shelly fossils have been found in the Lintiss Vale Formation to substantiate Wade's (1970) and Daily's (1973) assertions that the Lintiss Vale Formation is of Early Cambrian age. 3. The basement rocks of the Wonominta Block include a wide range of low grade metamorphics, (metagreywacke, schist, phyllite, quartzite and some maroon and green matavolcanics) all referred to the 'Precambrian' Wonominta Beds (Cooper, 1975). There are no known glacial deposits or trace-fossil assemblages to suggest latest Proterozoic or Vendian horizons. However, Edwards (1979) has inferred that some of the rocks included previously as basement in the Wonominta Block may have an Early Cambrian or Late Vendian age. Scheibner (1978, p.213) has argued that because the Wonominta Beds are intruded by the Tibooburra Granite of 650 Ma, they, are Precambrian in age. Crook (1980, p.227) on a similar basis has interpreted the Wonominta Beds as in part 'Adelaidean'. 4. Pogson & Scheibner interpreted the Copper Mine Range Beds as having formed during the Early Cambrian in deeper waters to the east of the Gnalta Shelf (on the 'White Cliffs Deeper Terrace'). However, the deposits lack any associated volcanic-derived material - as might be expected in an area adjacent to the Mount Wright area. It seems likely therefore that the Copper Mine Range beds have either a Middle Cambrian, or less likely, a latest Proterozoic-Vendian , age. 5. Tibooburra Granite Rb/Sr date 650 ± 30 Ma (S.Shaw, in Pogson & Schneiber, 1976, p.9) is now considered incorrect. Later analyses using biotite, have provided a mean age of 410 Ma (S.Shaw, pers. comm. 1978 to B.D.Webby).

ANTARCTICA

Nimrod Glacier - Queen Maud Mountains BSG Beacon Supergroup; contains palynomorphs of probable Early Devonian age at Table Mountain, South Victoria Land (Kyle, 1977). Bg Byrd Group (Cambrian): comprises the formations listed below. SI Shackleton Limestone. A small collection of archaeocyathids from beds within 1000-1300 m of the base of the formation, immediately north of the Nimrod Glacier, has been dated as lower Lena Stage (Late Early Cambrian, Hill 1964). However, archaeocyathids are found up to 5400 m above the base and may be as young as early Middle Cambrian,. Sf Starshot Formation; sandstone, shale and conglomerate equivalent to or younger than Shackleton Limestone. Includes rhyolite flows and conglomerate bands with limestone pebbles. The Dick Formation of Skinner (1965) is a probable correlative in the Byrd Glacier region. Dc Douglas Conglomerate. Massive conglomerate overlying the Shackleton Limestone or Dick Formation with possible slight unconformity. Contains shale and limestone clasts. Includes minor interbedded limestone in the upper part. Lg Liv Group (Cambrian). Comprises the Greenlee Formation of quartzite and phyllite overlain by the Taylor Formation of mafic and felsic volcanics (including ignimbrites), quartzite, marble and volcaniclastics (Stump, 1976; McGregor & Wade, 1969). The Fairweather Formation and Henson Marble (McGregor, 1965) are metamorphic equivalents.

Appendix—Antarctica Bmg

Beardmore Group (Upper Proterozoic) comprises thick sequences of closely-folded quartzofeldspathic metagreywacke, argillite, slate and hornfels with a dominantly meridional strike, forming the basement of the central Transantarctic Mountains. Three laterally equivalent metagreywacke formations are recognised, as well as overlying and underlying units.

Lgf

La Gorce Formation of the southern Queen Maud Mountains (Stump, 1976) with a Rb-Sr isochron of 742 ± 27 Ma, intruded by latest Proterozoic and Ordovician granitoids (Easton, 1970). Closer to the coast, the Duncan Formation (McGregor, 1965) is a more metamorphosed correlative.

Goldie Formation of the Nimrod-Beardmore-Shackleton Glaciers region (Gunn & Walcott, 1962) with a Rb-Sr isochron of 548 ± 28 Ma, intruded by Ordovician granitoids (Gunner, 1976).

Cobham Formation. Biotite schist, hornfels, marble and quartzite conformably underlying the Goldie Formation in the Nimrod Glacier region (Laird et al., 1971).

Wyatt Formation. Massive biotite-quartz-feldspar porphyry intruding the La Gorce Formation, and associated ash-flow tuff (ignimbrite) and volcaniclastic sediments conformably overlying the La Gorce Formation (Stump, 1976, in press). Rb-Sr isochron ages range from <788 ± 6 Ma (Faure et al., 1979) to 643 ± 14 (Faure et al., 1968).

Nimrod Group. Quartzofeldspathic gneiss, biotite-quartz schist, migmatite, marble, quartzite and amphibolite, forming uplifted basement blocks in the upper Nimrod Glacier region. Provides an early Proterozoic (1800-2100 Ma) Rb-Sr isochron (Gunner & Faure, 1972) and latest Proterozoic-Ordovician K-Ar whole-rock and mineral ages (Adams, Gabites & Grindley, in press). Deformed in at least two Precambrian orogenies (Grindley & McDougall, 1969; Grindley, 1972), the younger episode accompanied by migmatisation.

Northern Victoria Land LYg Leap Year Group includes the following three formations: Rc

Reilly Conglomerate, inferred to be an equivalent of Camp Ridge Quartzite.

Carryer Conglomerate, polymict conglomerate.

Crq

Camp Ridge Quartzite, with Arthrophycus, Cambrian-Ordovician?

Daedalus,

Scolithus, and ?Monocraterion.

Latest

Mariner Group, includes three formations:

Edlin Formation with arthropod trails.

Spurs Formation with late Middle (Lejopyge laevigata Zone) and early Late Cambrian (Idamean, Mindyallan) trilobites.

Euf

Eureka Formation with late Idamean or early post-Idamean trilobites, Ruzophycus Cruziana.

Sledgers Group is composed of (1) Molar Formation - marine volcaniclastic sediments with acritarchs at several horizons and ptychagnostic trilobites and inarticulate brachiopods in the uppermost beds, indicating an age range of Middle Cambrian (Cooper et al., pers comm.); (2) Glasgow Volcanics, mafic volcanics of the northern Bowers Mountains interstratified with Molar Formation to the south.

and

Rhs

Retreat Hills Schist. Biotite schist, hornfels and actinolite schist exposed in Mariner and Upper Rennick Glaciers (Riddolls & Hancox, 1968).

RBg

Robertson Bay Group (Upper Proterozoic or younger). Quartzofeldspathic metagreywacke, argillite, slate and hornfels with a dominantly northwest strike forming the basement of North Victoria Land (Harrington et al., 1967; Gair et al., 1969), east of the Rennick Glacier and Bowers Trough. Contains rare calc-silicate, marble, dolomite and quartzite layers. Vendian acritarchs have been recovered from the upper part of the group adjacent to the Bowers Trough, and Riphean? acritarchs from an unknown stratigraphic level on the Pennell Coast contains metazoan trace fossils at some horizons.

Priestley Formation (Upper Proterozoic) Quartzofeldspathic metagreywacke, schist and hornfels with thin marble, quartzite and calc-silicate layers, found as enclaves in the Ordovician granite complex south from the upper Rennick Glacier to Terra Nova Bay (Skinner & Ricker, 1968).

Appendix—Antarctica

The Berg Group of the Oates Coast (Solov'ev, 1960) is a probable correlative and contains Riphean acritarchs (Iltchenko, 1972). Wg Wilson Group (Upper Proterozoic?). Quartzofeldspathic gneiss and biotite-garnet schist with thin marble, calc-silicate and amphibolite lenses, more or less migmatised by Ordovician granitic intrusions, forming upfaulted basement blocks east and west of the Rennick Glacier, extending south to Terra Nova Bay (Klimov & Solov'ev, 1958; Sturm & Carryer, 1970; Dow & Neall, 1974). Includes the Rennick Group of Gair (1967). Three episodes of penetrative deformation are recognised in the Lanterman Range, adjacent to the Bowers Trough (Bradshaw et al., in press) where it is overlain unconformably by the Sledgers Group (Laird et al., unpubl.). The group may be partly a more metamorphosed 'infrastructure' to the Robertson Bay and Berg Groups; its relation to older Precambrian cratonic basement has yet to be ascertained. More varied lithologies (amphibolite, conglomerate, quartzite) in the Lanterman Range may signify an older Precambrian terrain. Tectonic, igneous and met amorphic events 1. Nimrod Group. Rb-Sr isotopic data indicate that Nimrod Group basement complex metasediments were isotopically homogenized 1980 ± 80 Ma ago, either at the time of initial sedimentation and diagenesis or the time of first deformation (overthrusting and recumbent folding) of Nimrod Group. (Gunner & Faure, 1972; Grindley 1972). Earlier K-Ar dates on amphiboles of 1000-1100 Ma (Grindley & McDougall, 1969) are probably due to excess argon (Adams, Gabites & Grindley, 1982). 2. Beardmore Orogeny (Grindley & McDougall, 1969). An Rb-Sr isochron on Nimrod Group metasediments of 600 ± 38 Ma (Gunner 1976) is considered to record the main phase of deformation of the Nimrod Group (F of Grindley, 1972). When older ages up to 1150 Ma due to excess argon are excluded, K-Ar dates on amphiboles of 580-600 Ma from Nimrod Group amphibolites and skarns are in essential agreement (Adams, Gabites & Grindley, 1982). 3. Ross Orogeny (Gunn & Warren, 1962). An Rb-Sr isochron on Goldie Formation slates of the Beardmore Group of 549 ± 28 Ma (Gunner, 1976) is considered to represent isotopic homogenization early in the Ross Orogeny. Concordant biotite-hornblende K-Ar ages for Nimrod Group gneisses of 510-540 Ma indicate major uplift of the basement complex to the west of the Ross orogenic belt in the Late Cambrian (Adams, Gabites & Grindley, 1982). 4. Granite Harbour Intrusives (Gunn & Warren, 1962). Widespread invasion of granitic plutons in the Ross orogenic belt throughout the Transantarctic Mountains provides K-Ar mineral dates of 460-510 Ma (McDougall & Grindley, 1965; Adams, Gabites & Grindley, 1982). Rb-Sr isochrons of 490 ± 17 Ma and 473 ± 6 Ma for the Hope and Ida granites of Southern Victoria Land (Gunner, 1976) and a concordant U-Pb date on sphene of 476 Ma (Gunner & Mattinson, 1975) are in agreement. Beardmore and Byrd Group Slates also give whole rock K-Ar ages within the range 450-500 Ma reflecting folding, widespread uplift and heating by granites in the Early Ordovician (Adams, Gabites & Grindley, 1982). 5. Wilson Group. An Rb-Sr analysis from the Rennick schists, a probable correlative of the Wilson Group gave a maximum model age of 785 ± 20 Ma assuming a low initial ratio of 0.704. (Faure & Gair, 1970). The uncertainty in the initial ratio could reduce the age significantly perhaps to as low as 500 Ma, the normal mean for K-Ar ages from the Wilson Group (Adams et al., 1982). 6. Beardmore Orogeny. The only evidence for late Precambrian or early Cambrian plutonic activity in North Victoria Land is a single K-Ar age of 555 Ma from a foliated granodiorite in the Wilson Group of the Oates Coast (Sturm & Carryer, 1970). Rb-Sr model ages of 785 ± 20 Ma for the Rennick Schist and 540 ± 13 Ma for gneissic granite from the same area (Faure & Gair, 1976) could be recording a latest Precambrian Early Cambrian orogenic event. 7. Ross Orogeny and Granite Harbour Intrusives. K-Ar whole rock ages on granites from the Oates Coast range between 430 and 490 Ma (Sturm & Carryer, 1970) using the new constants. Numerous K-Ar whole rock dates on slates (420-510 Ma) from the Robertson Bay and Sledgers Groups reflect widespread orogenic uplift and heating of basement rocks during the Ordovician (Adams et al., in press) perhaps contemporaneous with deposition of coarse clastics in the Bowers Trough (Leap Year Group of Laird et al., 1982). 2

Appendix—Tasmania

Borchgrevink Orogeny (Gair et al., 1969, Craddock, 1972). A mid-Paleozoic episode of deformation was originally inferred from K-Ar whole rock dating of Robertson Bay Group slates from the Pennell Coast (Sturm & Carryer, 1970). More thorough sampling of the Roberston Bay Group has provided K-Ar dates within the time range of the Ross Orogeny (460-510 Ma). However, younger Cambrian formations in the Bowers Trough (Mariner and Leap Year Groups) have provided K-Ar whole rock dates on slates within the range 390-430 Ma and are presumed to represent folding and/or major uplift during the Silurian and early Devonian.

Gallipoli Rhyolite. A single whole rock Rb-Sr model age on the Gallipoli Rhyolite in the Upper Rennick Glacier is not well determined at 382 ± 40 Ma (Faure & Gair, 1970) but may indicate an episode of Late Devonian volcanism comparable with eastern Victoria (q.v.).

10.

Admiralty Intrusives. The post-tectonic plutons intruding the Robertson Bay Group have provided K-Ar biotite and whole-rock ages within the range 300-385 Ma (Sturm & Carryer, 1970; Laird et al., 1974; Nathan, 1971) comparable with the late Devonian-early Carboniferous granitic intrusives of eastern Victoria, Tasmania and western New Zealand.

TASMANIA Smithton RCG

Rocky Cape Group - unmetamorphosed Precambrian quartzite and siltstone.

Smithton Dolomite - dolomite with rare stromatolitic horizons, black to grey chert, black slate. Basal siliceous conglomerate and quartzite.

Art

Arthur River sequence - basal diamictite with dolomite clasts, followed by spilite-greywackesiltstone-tuff sequence.

Christmas Hills sequence - siltstone, greywacke, basic volcanics, with late Middle Cambrian trilobites.

Dundas Trough TN

Tyennan Nucleus - regionally metamorphosed (lower to upper greenschist) quartzite-schistphyllite sequences.

Oonah Formation - comparatively unmetamorphosed quartzite-slate sequence of Zeehan area.

SCG

Success Creek Group - quartzite, mudstone, chert, minor carbonate sequence, unconformable on Oonah Formation.

Renison Bell sequence - siltstone-quartzite with carbonate-chert lenses, equivalent to upper part of Success Creek Group.

Ccf

Crimson Creek Formation - thick unfossiliferous sequence of mudstone, siltstone, greywacke, with spilite and chert in some areas; intruded by ultramafic-mafic complexes.

Dundas Group - fossiliferous Middle to Late Cambrian mudstone-greywacke-conglomerate sequence with minor acid and basic volcanics.

Rlc

Red Lead Conglomerate - chert-rich greywacke-conglomerate with ultramafic detritus in several areas.

Hsl

Hodge Slate - black slate with dendroids, hydroids, and agnostids of Middle Cambrian age.

Rbc

Razorback Conglomerate - chert-rich greywacke conglomerate.

Bjn

Brewery Junction Formation - lower laminated siltstone and fine sandstone with acid tuff lens, faulted against upper greywacke-siltstone with early Late Cambrian fossils.

Clf

Climie Formation - greywacke-mudstone with middle Late Cambrian trilobites.

Mic

Misery Conglomerate - siliceous pebble-boulder conglomerate with some graded sandstone beds; concealed possibly faulted or disconformable contact with over-lying Lower Ordovician sandstone. Mount Read Volcanics: complex belt of acid to intermediate and minor basic volcanics, partly Middle to Late Cambrian but age of base not known.

Appendix—Tasmania

80 TG

Tyndall Group - fossiliferous upper part of Mount Read Volcanics in Queenstown area; basal limestone with late Middle Cambrian fossils, upper unit rich in volcaniclastic conglomerate; locally overlies mineralised and altered volcanics.

Owen Conglomerate - siliceous Precambrian-derived conglomerate and sandstone, up to boulder grade, partly non-marine; trace fossils in places.

Ncs

Newton Creek Sandstone - lower marine (proximal turbidite) facies of Owen Conglomerate in Tyndall Range area; middle Late Cambrian fossils.

Pioneer Beds - sandstone and fine conglomerate forming upper part of Owen Conglomerate at Queenstown; tracefossils, shelly fossils, chromite-rich bands; gradational into overlying shale and limestone.

Gordon Limestone undifferentiated-equivalent to Gordon Subgroup.

Eldon Group.

Css

Crotty Sandstone - shallow-marine quartz sandstone, Llandovery age.

Ams

Amber Slate - late Llandovery age.

Keel Quartzite - poorly fossiliferous.

Aus

Austral Creek Siltstone - lower Ludlow age.

Fls

Florence Sandstone - richly-fossiliferous quartz sandstone with shelly faunas of Pridolian to possibly Early Devonian age.

Bsh

Bell Shale - extensive siltstone-mudstone-fine sandstone sequence with limestone lenses, Early Devonian shelly faunas.

Phi

Point Hibbs Limestone - thick coralline limestone within coarse clastic sequence at Point Hibbs; middle to late Siegenian age.

Dial Range - Fossey Mountains FN

Forth Nucleus - metamorphosed Precambrian similar to Tyennan Nucleus.

Burnie Formation - relatively unmetamorphosed but poly-deformed quartzwacke turbidite sequence forming eastern part of Rocky Cape Region; includes minor pillow lavas and dolerite dykes and sills.

Bac

Barrington chert - thick sequence of laminated grey, white and black chert regarded by Jennings (1979) as oldest part of Cambrian sequence in Sheffield area.

Msp

Motton Spilite - thick sequence of pillow lavas and massive spilite in Dial Range Trough; overlies Barrington Chert correlate.

Cateena Group - fossiliferous mudstone-greywacke-conglomerate sequence with minor acid tuff in Dial Range Trough; late Middle Cambrian fossils.

RaG

Radfords Creek Group - similar to Cateena Group, with chert and spilite detritus in lower part; late Middle and early Late Cambrian fossils.

Megabreccias of Dial Range Trough - unfossiliferous.

Duncan Conglomerate - chert-rich conglomerate derived from chert masses in Dial Range Trough, equivalent of Owen Conglomerate.

Mss

Moina Sandstone - widespread shallow marine quartzose sandstone in Dial Range and Fossey Mountains Troughs; trace fossils and shelly fossils.

Gordon Limestone sequence in Mole Creek area.

Eug

Eugenana Beds - undeformed cave deposits in folded Gordon Limestone at Eugenana quarry; late Middle Devonian spores.

Adamsfield TN

Tyennan Nucleus.

Appendix—Tasmania WRB JB Dph Fch Mx Wss Meg Fgm TRB DSG Sc Gds Rc Fv GSG Kgl Ccl Bjl Llm Lsm Ulm Als TRG Gq Ric Cuq Mcf

Wedge River Beds - interbedded bouldery diamictite, mudstone and sandstone at western margin of trough; recumbently folded. Jubilee Block - area of dominantly unmetamorphosed Precambrian rocks each of Tyennan Nucleus, with dolomite, siltstone, quartzite, quartzwacke, etc. Dolomite-phyllite sequence near north western margin of trough. Foliated chert-greywacke-mudstone sequence in northern part of trough - one of several probable tectonic wedges. Coarse mixtite with blocks of locally-derived lithologies as well as Precambrian quartzite. Wings Sandstone - tectonic lens of massive unfoliated quartzite with underlying red-bed sequence of siltstone and sandstone. Extensive mudstone-chert-greywacke sequence in southern part of trough, with minor basicintermediate volcanics on Gordon Road and at Mt Mueller. Fossiliferous greywacke-mudstone unit on Gordon Road with Middle Cambrian trilobites; probably a fault block. Trial Ridge Beds - basal siliceous conglomerate and cross-bedded sandstone, fossiliferous siltstone and quartzwacke in middle part (upper Middle Cambrian). Denison Subgroup - Late Cambrian to Early Ordovician regressive clastic sequence (3400 m) above widespread angular unconformity; equivalent to Owen Conglomerate. Singing Creek Formation - proximal quartzwacke flysch sequence with middle Late Cambrian fossils; ultramafic detritus at base at Adamsfield. Great Dome Sandstone - shallow-marine and deltaic sandstone and siltstone with abundant trace fossils; probably Late Cambrian. Reeds Conglomerate - siliceous Precambrian-derived pebble-cobble conglomerate and sandstone; largely non-marine; in wedges up to 1500 m thick. Florentine Valley Formation - richly-fossiliferous sandstone-siltstone-minor limestone sequence; Lower Ordovician. Gordon Subgroup - Ordovician limestone sequence in Florentine Valley; maximum thickness 2100 m; four formations. Karmberg Limestone - basal impure limestone with upper cherty member; probably of Castlemainian. Cashions Creek Limestone - Girvanella-rich limestone, Chazyan age. Benjamin Limestone. Lower Limestone Member - mainly Blackriveran age. Lords Siltstone Member. Upper Limestone Member - includes richly-coralline unit near top; Eastonian - Bolindian. Arndel Sandstone - upper sandstone-siltstone unit of Gordon Subgroup, incorporates Westfield Beds of Corbett & Banks (1974); shelly fossils and graptolites span Ordovician-Silurian boundary. Tiger Range Group - clastic sandstone-siltstone sequence (900 m +) in Tiger Range - Gordon Range area; correlate of Eldon Group. Gell Quartzite - unfossiliferous ripple-marked quartzite. Richea Siltstone - contains graptolites and shelly fossils of late Llandoverian age. Currawong Quartzite - interbedded quartzite and minor siltstone; shelly fossils indicate preDevonian age. McLeod Creek Formation - thick sequence of mudstone and fine sandstone, unfossiliferous; probably equivalent to Bell Shale.

Appendix—Victoria

Northeastern Tasmania MB Mathinna Beds - widespread folded sequence of mudstone and quartzwacke turbidites; fossils of Early Ordovician and Early Devonian age. Tectonic, igneous and metamorphic events 1. King Island granite - highly deformed syn-tectonic adamellite-granodiorite intruding strongly deformed quartzite-mudstone sequence on western part of King Island. Rb-Sr date of 735 Ma considered to be emplacement date (McDougall & Leggo, 1965). Oldest K-Ar date 725 Ma. 2. Frenchmans Orogeny - polyphase deformation with early main phase of metamorphism (upper greenschist facies) affecting rocks of Tyennan Nucleus. Early phase could be about 800 Ma old (Raheim & Compston, 1977). 3. 'Jukesian Movement' - unconformity in some areas between Owen Conglomerate and underlying volcanics. Contact with Tyndall Group is conformable in some places, unconformable in others. Probably mainly fault movements. 4. Haulage Movement - angular unconformity in upper part of Owen Conglomerate between regionally transgressive sandstone (Pioneer Beds) and underlying fault-controlled graben deposits. K-Ar dates of 470-490 Ma on slates from Mt Read Volcanics may record Early Ordovician uplift (Black & Adams, 1980). 5. Late Devonian - Early Carboniferous discordant granitic plutons of western Tasmania and King Island. Most dates (Rb-Sr and K-Ar) are in the range 345-370 Ma. (McDougall & Leggo, 1965.) 6. Cooee Dolerite - dykes and sills of sodic dolerite intruding Burnie Formation. Some dykes deformed by early-phase folds of Penguin Orogeny. K-Ar dates of 725 ± 35 (Richards, in Solomon & Griffiths, 1974) and 710 Ma (McDougall & Leggo, 1965) recorded. 7. Penguin Orogeny - multiphase folding of Burnie Formation; thought to be dated by syn-tectonic Cooee Dolerite dykes (see above) and K-Ar dates on slates of 670-690 Ma (Black & Adams, 1980). 8. Structural position of Barrington Chert (and Motton Spilite) in Dial Range Trough according to Burns (1964). Probably due to thrusting. 9. Intrusive intermediate dyke (in Radfords Creek Group) at Gunns Plains, with Rb-Sr whole-rock isochron age of 480 ± 1 8 Ma (Jago, Cooper & Corbett, 1977). Possibly equivalent to Lobster Creek Volcanics, a large igneous mass in core of trough. 10. Widespread folding correlated with Tabberabberan. Upper age limit given by undeformed Eugenana Beds (late Middle Devonian). K-Ar dates on folded slates in western Tasmania of 400-430 Ma (Black & Adams, 1980; C.J.Adams, pers. comm.) and Rb-Sr dates of 400-425 Ma on Mathinna Beds (Cocker, 1977). 11. Possible tectonic movement in Adamsfield Trough separating foliated sequences from unfoliated sequences. Most units in this trough are tectonic wedges. 12. Extensive Upper Devonian - ?Lower Carboniferous discordant granitic plutons in eastern Tasmania and Flinders Island. Oldest dates for Scottsdale and Blue Tier 384 and 395 Ma (McDougall & Leggo; Cocker, 1965,1977). Ranges for all northeastern granites are: Rb-Sr 345395, K-Ar 349-384 Ma.

VICTORIA

Glenelg Sedimentary Belt Grb Glenelg River Beds: unfossiliferous quartz sandstone, slate and minor lithic greywacke, black slate, dolomitic limestone and slate, and volcaniclastics, deformed before intrusion of the Early Ordovician Wando Granodiorite Sg Mount Stavely Complex: andesitic to rhyolite lavas and tuffs with minor interbedded chert, siltstone and intruded serpentinite. Correlated with the Lower Cambrian Heathcote Greenstone. Glenthompson Beds: arkosic sandstone and mudstone post-dating Stavely Complex. Gt

Appendix—Victoria GWC Rr.Wr

Sedimentary bedrock of the Glenthompson-Wickliffe-Chatsworth area. Rocklands Rhyolite, Wickliffe Rhyolite: they are assumed to be age correlatives. The Rocklands Rhyolite intrudes basement sediments and overlies the basal Ordovician Wando Granodiorite; it underlies Upper Devonian sediments in the Black Ranges and, probable Upper Silurian Grampians Group in the Grampians Ranges. Pebbles of Wickliffe Rhyolite are present in basal Grampians Group conglomerate. Age is tentatively taken as Silurian. Grampians Group, comprised of four formations. In upward sequence: Redmans Bluff Sandstones, Silverband Formation, Mount Difficult Sandstones and Victoria Range Sandstones. Late Silurian to earliest Devonian age inferred from age of intruding granites . ( G W C )

(2)

(4)

Stawell Sedimentary Belt Ag Greenstone outcrops on Mt Ararat: actinolite schist, amphibolite and hypersthene-bearing gneiss. Mg Magdala Sandstone: 'greenstone' intersected in Western Mining Corporation drillhole, thought to represent albitised basic volcanics and correlated with Ararat Greenstone . Sa St Arnaud beds: a thick unfossiferous succession of turbiditic greywacke and slate. (Ag)

Bendigo Sedimentary Belt RG Romsey Group: lithic and quartzose sandstone ('proximal' turbidites) and siltstone alternating with black and grey siliceous shale; graptolites of Lal-Be4 zone age. Olm Undifferentiated: similar to RG but showing upward decrease in sandstone abundance and containing a complete graptolite sequence from La2 to Da3 zone age. Heathcote Belt Hg Heathcote Greenstone: volcanics, volcaniclastics, shale, chert, shale breccia, and intrusives. Volcanics are meta-andesite at Heathcote, metabasalt north of Heathcote and at Lancefield. Intrusives consist of altered dolerite dykes and rare small patches of peridotite, pyroxenite, serpentinite, and talc schist. Interbedded shale and chert contain radiolaria and sponge spicules, including Protospongia (Thomas et al., 1967). Trilobites including a protolenid occur at two localities in volcaniclastic sediments and indicate an Early Cambrian age (P.A.Jell, pers. comm.). Td Unnamed fault-bounded lens, surrounded by Hg, of sheared and altered greenstone-derived clastics, with a thin calcareous band containing shelly fossils, including archaeocyathids, of late Early or early Middle Cambrian age (O.P.Singleton, pers. comm.). Ms Monegeetta Shale: 200 to 580 + mof black shale, mudstone, siliceous shale, with interbedded volcanogenic sandstone, overlying Heathcote Greenstone with concordant and apparently conformable contact. Contains rich Middle Cambrian dendroid fauna and algae, and rare brachiopods and trilobites (VandenBerg & Wilkinson, in prep.). Ke Knowsley East Formation (Thomas & Singleton, 1956). Gc Goldie Chert: 190 to 290 + mof unfossiliferous varicoloured chert, rare chert-breccia, and insignificant shale. This unit appears to be restricted to the Lancefield area, and rocks previously classed as 'Goldie Shale' at Heathcote are here regarded as Monegeetta Shale or Knowsley East Formation (VandenBerg & Wilkinson, in prep.). Oh Ordovician of Heathcote Belt: small fault blocks and slivers of Ordovician sediments are incorporated in the structurally complex central segment of the Heathcote Belt near Heathcote (Thomas, 1956). They are incomplete, and in disrupted, apparently random sequence, ranging in age from Lancefieldian to Gisbornian. They consist of quartzose greywacke (turbidites), mudstone, and black shale. Melbourne Trough Ba Jamieson Greenstone of Barkly River Belt: unknown thickness of meta-andesite, volcaniclastics, shale, and small fault-bounded blocks of altered limestone (Dunn, 1974).

Appendix—Victoria

Howqua Shale: black shale, siliceous shale, phosphatic sandstone with La2 graptolites and shelly fossils restricted to fault-bounded patches near Mansfield and Licola (Howitt, 1923; VandenBerg, 1978). A little-known outcrop at Boolarra contains La3 graptolites (Keble, 1920).

Ordovician of Mornington Peninsula: the Lower Ordovician (La2 to Yapeenian) appears to be similar to that of the Bendigo Sedimentary Belt. The Middle and Upper Ordovician are poorly documented and appear to be condensed (Keble, 1950; Hills & Thomas, 1954).

Riddell 'Grits': quartz-rich turbiditic sandstone, mudstone and shale, with Darriwilian (Da3 and Da4) to Eastonian graptolites and rare comminuted shelly fossils. Thickness is probably in excess of 1 km.

Unnamed Bolindian: unknown thickness of mostly thin-bedded black shale, black mudstone, sandstone. Only the upper part (equivalent to the British D. anceps Zone) outcrops widely and contains Dicellograptus ornatus, D. o. minor, Climacograptus latus, C. pacificus, several subspecies of C. longispinus, C. hastatus, and Plegmatograptus (?) n.sp., together with rare Pleurograptus linearis. The shales are overlain by about 20 m of sparsely bioturbated siltstone with Dalmanitina (D.) darraweitensis, Glyptograptus cf. tamariscus, and Climacograptus cf. normalis (VandenBerg, MS).

Mount Easton Shale (VandenBerg, 1975), with rich and diverse graptolite faunas ranging from Darriwilian (Da3) to late Bolindian.

Deep Creek Siltstone, Costerfield Siltstone: up to 800 m of siltstone, often intensely bioturbated. The largely undescribed graptolite fauna includes Akidograptus cf. acuminatus, Climacograptus cf. scalaris, C. miserabilis, Rastrites linnaei, and monograptids of the M. turriculatus Zone at the top (see VandenBerg et al., 1976).

Springfield Formation, Wapentake Formation, Chintin Formation: up to 1000 m of siltstone with abundant 'proximal' turbidites, channel-filling sandstone, conglomerate, pebbly mudstone, with late Llandoverian graptolites and shelly fossils (see VandenBerg et al., 1976).

'Kilmore Beds': very thick monotonous siltstone, largely unfossiliferous. Age probably ranges from Wenlockian to Ludlovian. Possibly synonymous with Dargile Unit 1 of Thomas (1937) (VandenBerg MS).

Anderson Creek Formation (VandenBerg, 1971; VandenBerg et al., 1976).

Dargile Formation (VandenBerg, 1971.; VandenBerg et al., 1976).

Mclvor Formation (see VandenBerg et al., 1976).

Mount Ida Formation (see VandenBerg et al., 1976).

Humevale Siltstone (Williams, 1964; see VandenBerg et al., 1976).

Lilydale Limestone; this unit is here regarded as an autochthonous lens (contra VandenBerg et al., 1976), and contains bands of oxidised limestone and mudcracks.

Yeringberg Sandstone*-Caw Hill -Sandstone: these two units are here regarded as probable correlates, even though the Cave Hill Sandstone rests with slight angular unconformity on the Lilydale Limestone (Crohn, 1953). The Yeringberg Sandstone overlies black shale (probably Wilson Creek Shale) and contains a rich Pragian shelly and dacryoconarid fauna. (See VandenBerg, 1975).

Jordan River Group (VandenBerg, 1975) comprising Ma McAdam Sandstone Bu Bullung Siltstone Si Sinclair Valley Sandstone Ws Whitelaw Siltstone Bo Boola Formation (Philip, 1962; but see also VandenBerg, 1975) Es Eildon Sandstone Wi Wilson Creek Shale Cc Coopers Creek Limestone (Philip, 1962)

Walhalla Group (VandenBerg, 1975), comprising No Norton Gully Sandstone Mh Montys Hut Formation Li Liptrap Formation (Lindner, 1953; Singleton, 1967).

Appendix—Victoria CB MU

Cathedral Beds (VandenBerg et al., 1976; VandenBerg, 1978) Mount Useful Slate (VandenBerg, 1978).

Mount Wellington Belt Wa Unnamed metabasalt, including pillow lava, and interbedded sediments intruded by partly serpentinized peridotite; contains infaulted limestone lenses near the eastern boundary fault (Lindner, 1953; Singleton, 1967; Crawford & Keays, 1978). Ja Jamieson Greenstone (the more commonly used name 'Wellington Greenstone' clashes with several other formation names); metabasalt, volcaniclastics, and chert intruded by metadolerite sills, and metamorphosed to greenschist facies. Thickness is in the order of 3 km. (Teale, 1919, 1920; Crawford & Keays, 1978). Wr Unnamed ultramafic and mafic intrusives; throughout the Mount Wellington Belt, the metabasalts are intruded by various types of peridotite (largely serpentinised or altered to talc rock) and gabbro (Teale, 1920; Boxer, 1973; Vinycomb, 1973; Crawford & Keays, 1978). Gf Garvey Fully Formation (Thomas & Singleton, 1956; Teale, 1920). Restricted to Wellington River area. Do Dolodrook Limestone; intercalated in Gf (Thomas & Singleton, 1956). Hs Howqua Shale; apparently restricted to the Howqua River area (Harris & Thomas, 1938a). Di Digger Island Limestone; (Lindner, 1953; Singleton, 1967). Me Mount Easton Shale (see Melbourne Trough). W1 Waratah Limestone (Lindner, 1953; Singleton, 1967); contains Eognathodus sulcatus (Philip & Pedder, 1968). Ep Bell Point Limestone (Talent, 1965b; Singleton, 1967), contains early Emsian brachiopods (Talent, 1956a). Eastern Victoria Ho Lower Ordovician of upper Howqua River (Harris & Thomas, 1938a). Hb Hotham Beds: thick sequence of turbiditic sandstone, mudstone, some black shale, and rare chert. Graptolites range from late Middle Ordovician (Da4) to late Eastonian west of Kiewa Fault, and from Gisbornian to late Bolindian east of Kiewa Fault. Mm Mitta Mitta Volcanics (Talent, 1965b; VandenBerg et al., 1976). Tv Thorkidaan Volcanics (VandenBerg et al., 1982). Thick sequence of ignimbritic, probably partly marine rhyolite with some rhyodacite and andesite, often strongly foliated and metamorphosed to chlorite grade (greenschist facies). Contacts with Ordovician metasediments are faulted. Eg Enano Group (VandenBerg et al., 1982). Consists of three formations: 1 - Gibsons Folly Beds: unknown thickness of unfossiliferous interbedded volcanics (rhyolite through andesite and rare basalt) and sediments (mudstone, volcanogenic and sedolithic conglomerate, tuff, agglomerate); 2 - Towanga Formation: unknown thickness of turbiditic quartzite and mudstone with lenses of conglomerate, rhyolite, rhyodacite, and marble; 3 - Cowombat Formation: unknown thickness of marine mudstone with lenses of limestone, marble, and rare volcaniclastics, with occasionally rich Ludlovian shelly and conodont faunas (Talent et al., 1975). Enano Group rocks are generally highly cleaved and foliated, and metamorphosed to chlorite grade (greenschist facies). Internal stratigraphic relationships, and relationship with Tv, are unclear. Contacts with Ordovician metasediments are faulted. Wc Wombat Creek Group (VandenBerg et al.., 1976) applies to Wombat Creek section only Jr Jemba Rhyolite (Brooks & Leggo, 1972). Ss Seldom Seen Group (VandenBerg & O'Shea, 1981). Sr Snowy River Volcanics (Ringwood, 1955; Fletcher, 1963; Bradley, 1969; Lenard, 1976).

86 We Bg Cv

Appendix—Victoria

Wentworth Group (Talent, 1963; VandenBerg et al., 1976). Buchan Group (Teichert & Talent, 1958; VandenBerg et al., 1976). Cerberean, Acheron and other acid volcanic complexes in circular cauldron structures within Melbourne Trough (Hills, 1959). Interbedded lacustrine sediments e.g. Taggerty Group with fish and plant remains mainly of late Givetian and Frasnian age. K-Ar age determination of 367 ± 5 Ma on Snobs Creek Volcanics below Taggerty Group. Bv Boyd Volcanic Complex (Fergusson et al., 1979). Acidic lavas and minor mafic lavas. Fish and plant remains in interbedded lacustrine and fluviatile sediments. ARg Avon River Group (Talent, 1963; Talent & Banks, 1967; Webby, 1972). Non-marine sediments with acidic volcanics, some in cauldrons. Mg Mansfield Group (Howitt Trough). Merrimbula Group (SE Victoria). Non-marine red beds and quartzose sandstone sequences. Late Devonian fish and plant remains. Tectonic, igneous and metamorphic events 1. Intrusions into Grb include dykes (?) of meta-dolerite, amphibolite, serpentinised peridotite, and pods of serpentinite and meta-gabbro (or pyroxenite) (Wells, 1956). There is no real evidence for correlating these with Lower Cambrian 'greenstone' (as suggested by Thomas et al., 1976). Rather, the rocks may represent several distinct igneous events, with amphibolite and meta-dolerite flows? possibly contemporaneous with, and ultramafic dykes post-dating, Grb. 2. Folding and metamorphism of Grb to schist and gneiss of up to almandine amphibolite facies (Wells, 1956). At Glenelg River, sillimanite-muscovite-biotite gneiss is K-Ar dated at 512 ± 9 Ma, (C.J.Adams, pers. comm.). Intruded by foliated and unfoliated granitoids with K/Ar biotite ages of 490-480 Ma (Bowen 1975; Richards & Singleton, 1981), which suggests the deformation is Delamerian (Late Cambrian). 3. Bindian Orogeny (= Bowning Orogeny in New South Wales) produced tight folding and metamorphism in Wc, Eg, Tv apparently associated with intrusion of Kosciusko Batholith (KAr age of 415 ± 8 Ma at Deddick River; Bowen, 1975). Moderate folding of Gg may belong to this phase, which was followed by (4). 4. Widespread intrusion of granitoids with K/Ar age of 405-400 Ma (e.g. granitoids at MacKenzie River, Glenelg River, Wycheproof, Mount Kooyoora, Mount Hooghly, Mount Buffalo, Dargo) (Bowen, 1975; Richards & Singleton, 1981). 5. Tight folding and metamorphism of GWC and Sa to phyllite and schist of up to biotite facies is provisionally correlated with (2) but may be as young as Late Ordovician - earliest Silurian. Sa exhibits folded cleavage and folded quartz veins. 6. Ballarat-Wedderburn Line marks westernmost limit of Ordovician graptolites, apparently coincident with abrupt change of average strike from about 330° in Sa to about 345° in Olm. 7. Beavis (1967) postulated that folding of Olm began during sedimentation, and that faulting was responsible for cessation of deposition west of the Muckleford Fault in about Chewtonian time. 8. Age of deformation and metamorphism of Olm up to greenschist facies is not known with precision, but is tentatively correlated with (20). 9. Western boundary of Heathcote Belt is faulted in most places, with the greatest structural complexity concentrated near Heathcote. An apparently complete Lower Cambrian to Lower Ordovician sequence occurs at Lancefield. 10. Mount William - Mount Ida Fault forms tectonic contact between Heathcote Belt and Melbourne Trough sequence. The fault is near-vertical, and has a total vertical displacement of 10-15 km at Heathcote. the Riddell Grits (here placed in the Melbourne Trough) extend acrolm is tectonic (Djerriwarrh Fault). 11. The Darraweit Guim Province is depicted in three columns; the left column represents the western marginal sequences (Heathcote - Keilor), the middle column the northeastern region (Yea - Seymour), the right column the southeastern region (Melbourne - Lilydale).

Appendix—New 12. 13.

14.

15. 16. 17. 18. 19. 20.

21. 22. 23. 24. 25.

Zealand

The boundary between the Darraweit Guim and Mount Easton Provinces is here taken as a line between Killingworth and Warburton. The actual boundary shifted with time, and the Upper Ordovician of Mornington Peninsula and Yeringberg Sandstone near Lilydale belong in the Mount Easton Province. Tabberabberan Orogeny, a widespread Middle Devonian deformation which produced tight folding and metamorphism to greenschist facies in the Melbourne Trough and Wentworth Group, and moderate folding accompanied by block faulting in other parts of eastern Victoria. The gentle unconformity below Ye at Lilydale suggests that folding began in the middle Early Devonian. Oldest post-Tabberabberan intrusions in Central Victoria have K/Ar ages of 387-384 ± 14 Ma (Woods Point Dyke Swarm, Mount Buller Granodiorite; Richards & Singleton, 1981). Granitoids in western and eastern Victoria have a somewhat broader range (395 ± 8 to 386 ± 6 Ma) (Mafeking, Llar-ne-gerin, Ben Nevis in western Victoria; Genoa Peak, Murrungowar, Errinundra, Yackandandah Basin, Beechworth and Everton in eastern Victoria) (Bowen, 1975, Richards & Singleton, 1981). Faulted boundary separates Waratah Bay Belt and Melbourne Trough sediments. Uplift is inferred from deposition of shallow water carbonate and clastics, and from presence of 'greenstone' - derived clastics in Bo. Complex tectonic boundaries separate Mount Wellington Belt from Melbourne Trough sediments. At Howqua River, the Mount Wellington sequence passes eastwards into sparsely fossiliferous Lower Ordovician containing Bendigonian graptolites. The (faulted) eastern boundary of the Mount Wellington Belt represents a drastic facies change from condensed black shale (Me) to thick sandstone and mudstone (Hb). Benambran Orogeny; best documented in eastern Victoria, where it produced tight folding of Hb, and metamorphism to schist and gneiss of up to amphibolite facies (Omeo Metamorphic Complex; Crohn, 1950). The tightest fossil control places it between late Bolindian and Ludlovian. Rb/Sr and K/Ar dates of 435-430 Ma from associated granitoids are thought to date the deformation (Brooks & Leggo, 1972; Richards & Singleton, 1981). High level plutons intruding cauldron lavas of Melbourne Trough. Post-tectonic, unstressed contact aureoles. (Hills, 1959.) Numerous K/Ar dates in range 360-375 Ma. Warby Range Granodiorite and other subvolcanic plutons intruding Avon River Group. K/Ar dates 370-380 Ma. Gabo Island Granite and other subvolcanic alkaline granites intruding Boyd Volcanic Complex. K/Ar dates 350-375 Ma (Fergusson et al., 1979). East of the Omeo Metamorphic Belt, the sparsely fossiliferous Ordovician - Silurian Hotham Beds have recently yeilded Early Ordovician (Bendigonian) graptolites at one locality near Eskdale in the Mitta Mitta Valley (Kilpatrick & Fleming, 1980). Upper Devonian; fresh-water sediments in the Black Ranges containing amphibian trackways, formerly considered part of Grampians Group.

NEW ZEALAND

Western Belt Rg Reefton Group, unconformable on Lancefieldian; contains middle to late Pragian fossils (Allan, 1935, 1947; Strusz, 1972). A Formation A' of Cooper (1979b); Gisbornian graptolites. Sc Slaty Creek Formation of Cooper (1979b); Dai-Gil graptolites. Aa Aorangi Mine Formation; La2 to Ya2 graptolites (see note 1). 4

88 W Gg

Appendix—New Zealand

Webb Formation; possible equivalent of Greenland Group. Greenland Group; La2 graptolites at Reefton; faulted/unconformable contact with Charleston Gneiss (Hume, 1977). Gp, Gd Peel and Douglas Formations with Gisbornian graptolites (in Gp). G1 Leslie Formation with graptolites of Gisbornian, Darriwilian and Bendigonian age. Ar Roaring Lion Formation. Cg Charleston Gneiss, Rb-Sr whole rock isochron date 680 ± 21 Ma (Adams, 1975). Precambrian paragneiss is present in the Victoria Range (A.Tulloch, pers. comm.). Mafic orthogneiss of granulite facies in Fiordland may be Precambrian (Oliver & Coggon, 1979) or lower Paleozoic (Wood, 1962, 1972). Central Belt Pb Baldy Formation. Ps Summit Limestone; contains Early Arenigian conodonts (Cooper & Druce, 1975). Pp Patriarch Formation; contains Tremadocian trilobites. Ha Anatoki Formation, includes interbedded volcanics. Tf 'Thompson's Flat Formation' of Farmer (1967), at Springs Junction; contains Late Cambrian trilobites (see note 4). HI Lockett Conglomerate; contains reworked Cobb Igneous Complex (Hunter, 1975). Ht Tasman Formation; contains late Middle Cambrian trilobites (Ptychagnostus punctuosus to Lejopyge laevigata Zone). Hd Devil River Volcanics; includes mafic intrusives and much volcanoclastic sediment. He Cobb Igneous Complex, comprising serpentinite, pyroxenite and gabbro (Hunter, 1977). Hb Balloon Formation; contains Vendian - Early Cambrian acritarchs. Eastern Belt Bb Baton Formation; contains late Siegenian - early Emsian? brachiopod fauna (Shirley, 1938); unconformable on Wangapeka Formation. Ef Fowler Formation. Eh Hailes Quartzite (includes Ellis Formation of Grindley, 1961, 1971). Ma2 Arthur Marble 2; contains latest Ordovician (Bolindian equivalent?) corals and conodonts. Mai Arthur Marble 1; contains Middle Ordovician conodonts; regional distribution and distinction from Ma2 still uncertain. Mw Wangapeka Formation; contains Eastonian graptolites. Mo Owen Formation (Coleman, in press) underlies Arthur Marble 1. Af 'Alfred Formation' of Farmer (1967); pelitic beds containing late Gisbornian or Eastonian graptolites (see note 4). Sf 'Sluice Box Formation' of Farmer (1967); limestone containing conodonts of Middle and probably Early Ordovician age. Tectonic igneous and metamorphic events 1. Left side of column represents the Aorangi Mine sequence described by Cooper (1979b). 2. Right side of column represents the Cobb-Roaring Lion sequence (Grindley, 1961, 1971; Skwarko, 1962). 3. Greenland Group is separated from the rest of the Ordovician Western Belt by the elongate Karamea/Tuhua Batholith.

Appendix—New 4. 5. 6. 7. 8. 9. 10.

Zealand

The Alfred', 'Sluice Box', and 'Thompson's Flat' Formations comprise a sequence confined to the Springs Junction/Lake Daniells area adjacent to the Alpine Fault. Tuhua Orogeny, main phase (F2 of Grindley, 1971); a. Granites emplaced in Western Belt sequence give concordant mineral and whole rock Rb-Sr ages of 350 and 365 Ma. (Aronson, 1968) and 380-390 Ma. (C.J.Adams, pers. comm.). Greenland Event; folding, cleavage formation, and low grade metamorphism of Greenland Group sediments in latest Ordovician Silurian (Adams et al., 1975). a. Granites emplaced in Western Belt sequence give Rb-Sr model ages of 410-430 Ma (C.J.Adams, pers. comm.). Thermal event producing Charleston Gneiss, Rb-Sr whole rock isochron 680 ± 20 Ma (Adams, 1975). Haupiri Disturbance, produced the Lockett unconformity and the coarse Locke tt Conglomerate; Cobb Intrusives detritus in Lockett Conglomerate. Baton Unconformity, first phase of Tuhua Orogeny (Fl) of Grindley (1961, 1971). Rameka Diorite of Riwaka Igneous Complex, post-dating Tuhuan folding (F2), gives an age of 367 ± 4 Ma (Harrison & McDougall, in prep.).

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