SIXTH INTERNATIONAL SYMPOSIUM ON THEORDOVICIAN SYSTEM

GUIDEBOOK FOR FIELD EXCURSION 3

ORDOVICIAN BASINS, VOLCANOES ANDSHELVES,

SOUTHERN AND CENTRAL NEW SOUTH WALES

by

D. Wyborn, L. Sherwin, B.D. Webby, R.S. Abell and I.G. Percival

RECORD 1991/50BUREAU OF MINERAL RESOURCES, GEOLOGY AND GEOPHYSICS

CANBERRA

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Refer to this publication as:WYBORN, D, SHERWIN, L., WEBBY, B.D., ABELL, R.S., & PERCIVAL, I.G., 1991.Ordovician basins, volcanoes and shelves, southern and central New South Wales: SixthInternational Symposium on the Ordovician System, Guidebook for Field Excursion 3.Bureau of Mineral Resources, Geology and Geophysics, Record 1991/49

© Commonwealth of Australia, 1991This work is copyright. Apart from any fair dealing for the purposes of study, research,criticism or review, as permitted under the Copyright Act, no part may be reproduced by anyprocess without the written permission of the Director, Bureau of Mineral Resources, Geologyand Geophysics. Inquiries should be directed to the Principal Information Officer, BMR, GPOBox 378, Canberra ACT 2601.

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Figure 1 (after Webby, 1976)

A. SUMMARY OF ITINERARY

Monday 8 July 1991

Participants arrive in Canberra; local sightseeing late afternoon

Overnight accommodation in Canberra: Forrest Motor Inn.

Tuesday 9 July 1991 . Canberra area

STOP 1 Ginninderra DriveSTOPS 2- 8 Section through quartz-rich greywacke-shale sequence. Bendora Pipeline RoadSTOP 2 Contact of sediments with Shannons Flat GraniteSTOP 3 Exposure of thrust rampSTOP 4 Overturned greywackes with sandstone dykeSTOP 5 View of Tidbinbilla PeakSTOP 6 Lunch on Cotter River. Contorted, cleaved black shales.STOP 7 Section through greywacke sequence. Convolute beddingSTOP 8 Section across reclined anticline, into black graptolite shale and overturned greywackeSTOP 9 State Circle Unconformity near Parliament House.

Overnight accommodation: Forrest Motor Inn. Dinner at the Inn.

Wednesday 10 July 1991 - Canberra-Goulburn -Cowra

STOP 1 Glenlee black shale quarry, MurrumbatemanSTOP 2 Calcareous concretions in greywacke, Gundaroo CreekSTOP 3 Hornfelsed greywacke, Federal Highway

Lunch at Goulburn

STOPS 4-6 Goulburn roadcuts, Ordovician and Silurian graptolitesSTOP 7 Roadcut on highway west of Jerrawa - Turbidite beds, GR 890446 Gunning 1:100000.STOP 8 Kenyu Formation - Volcaniclastic facies, GR 631137 Boorowa 1:100 000

Overnight accommodation: the Cowra Motor Inn. Dinner at the Inn

Thursday 11 July 1991. Cowra - Cliefden Caves - Cowra

STOP 1 Pillow lavas, Walli Andesite (Mower Ordovician), Limestone Creek.STOP 2 Cliefden Caves, near "Boonderoo" homestead geological and geomorphic introductionSTOP 3 Fossil Hill, Belubula River. Contact with Walli Andesite, and examination and collecting

from the Gleesons, Kalimna, Wyoming and Taplow Members of the overlying FossilsHill Limestone (Upper Ordovician).

STOP 4 Dunhill Bluff, Belubula River. Study of Taplow to Dunhill Bluff Members of the FossilHill Limestone.

STOP 5 West Boonderoo Shearing Shed - 'reefal' facies in the unhill Bluff Member of the FossilHill Limestone.

Picnic lunch, west bank of the Belubula River

4

STOP 6 Coppermine Creek at confluence with the Belubula River - lower part of the MalongulliFormation (Upper Ordovician)

STOP 7 Trilobite Hill, Belubula River - succession through the upper Belubula Limestone,Vandon Limestone and the basal Malongulli Formation (Upper Ordovician).

Overnight accommodation: Cowra Motor Inn, Cowra.Friday 12 July - Cowra-Orange-Parkes

STOP 1 Folded quartz greywacke, Nuneham ParkSTOP 2 Volcaniclastic sequence, RockvilleSTOP 3 Pillow lavas, Mount Pleasant VolcanicsSTOP 4 Junction Reefs Gold MineSTOP 5 Volcanic conglomerate Burnt Yards area

Lunch in Orange

STOP 6 Cheesemans Creek Formation, Keenan's quarrySTOP 7 Bowan Park Group, Quondong

Overnight accommodation: Court Street Motel, Parkes

Saturday 13 July - Parkes area

STOP 1 Yarrimbah Chen - early OrdovicianSTOP 2 Currajong Park - Goonumbla Volcanics, Gunningbland ShaleSTOP 3 New Durran - Goonumbla Volcanics, Gunningbland ShaleSTOP 4 Nelungaloo - Billabong Creek Limestone

Barbeque lunch at Nelungaloo Station.

STOP 5 Cotton Formation, Bolindian - TSR quarrySTOP 6 Cotton Formation, Bolindian - Burrawang RoadSTOP 7 Cotton Formation, LLandovery - Cottons Hill

Overnight accommodation: Court Street Motel, Parkes

Sunday 14 July - Parkes-Blue Mountains-Sydney

STOP 1 Visit to Geopeko Mine Office

Travel to Sydney stopping for site seeing in the Blue Mountains.

5

Figure 2 (after Vandenberg & Webby, 1988)

Map showing the distribution of Ordovician and Silurian rocks in central and southern NewSouth Wales,

6

B. INTRODUCTION (Webby and Wyborn)

Extensive areas of Ordovician sedimentary and volcanic successions occur in the Lachlan FoldBelt of central and southern New South Wales (Figs.1-2). Mostly these occupy complexly foldedand faulted, meridionally to NNW-trending belts. To the west, there is the relatively broad belt (orterrane) of the Wagga Metamorphic Belt, which seems to comprise a comparatively unifiedsequence of Lower Ordovician (Bendigonian, Darriwilian) to Upper Ordovician quartz-richgreywackes, siltstones, slates and cherts. These were uplifted, folded and regionallymetamorphosed in the latest Ordovician-early Silurian Benambran Orogeny. The major GilmoreFault now delineates the eastern margin of the Wagga Metamorphic Belt (Figs.2&4). TheOrdovician successions in the Wagga "Trough" have been interpreted as representing depositswhich accumulated in a marginal sea, like the present Sea of Japan (Webby, 1976; Cas 1983;Powell, 1984), but alternatively they may be viewed as a part of a more extensive "craton-derivedturbidite wedge" (Fergusson, 1991).

It is now apparent that at least a part of the extensive, poorly exposed developments of low grademetamorphics (mainly quartz rich greywackes, slates, schists, phyllites and cherts) of theGirilambone Group near Cobar is equivalent in age (Fig.2). Stewart and Glen (1986) haverecorded late Darriwilian-early Gisbornian conodonts from cherts in one area, which helps todispel earlier views that much of this complex was composed of a pre-Ordovician basement(Packham, 1969; Scheibner, 1972, 1973). The Giralambone Group may have some sort ofcontinuity with the Wagga Metamorphic Belt across the Gilmore Fault.

Cambrian rocks in the Lachlan Fold Belt have only been well documented from the regions of theHeathcote and Mt Wellington Axes, Central Victoria (Fig. 1). In New South Wales there is onlyone proven record of Cambrian deposits. Middle-Late Cambrian fossils have been recorded fromlimestone clasts in a basaltic breccia deposit in the Wagonga Beds, on the south coast of NewSouth Wales (Bischoff and Prendergast 1987). These deposits are presumed to be part of an exoticterrane, derived from a seamount, and incorporated in an accretionary prism (or melange) duringLate Ordovician times. The Wagonga Beds also include Late Ordovician graptolitic black shalesand cherts which are thought by Powell (1983) to have formed on the fringes of an abyssal plain.There are separate associations of Ordovician quartz-rich greywackes and slates on the coast, andquartz rich greywackes and shales inland, which Powell (1983) has interpreted as outer-arc slopeand fore-arc basin deposits, respectively. These are a part of an extensive development of quartz-rich turbidite and shale deposits included in the Monaro Basin (or Trough of Scheibner, 1972).This element is shown in many palaeogeographic reconstructions to lie to the east of the mainOrdovician volcanic island arc (Fig.3). Alternatively, Packham (1987) has interpreted, as aconsequence of suggested major post-Ordovician sinistral displacements in the Lachlan Fold Belt,that an extensive part of the quartz-rich turbidite facies of the Monaro Trough (except for a forearczone along the south coast) are back-arc deposits, like those of the Wagga Trough (Fig.4)

Palaeocurrent directions in the quartz-rich turbidites all indicate a southern (Antarctic) provinence.The graptolitic deposits of Late Ordovician age in the Canberra area belong to this association.Recently Glen et al. (1990) provided evidence to suggest that most of the quartz-rich greywacke inthe Monaro Trough is only of Early Ordovician age, and that the Late Ordovician is dominated bya starved graptolitic black shale. Where these two lithologies are in contact they are interleaved bythrust faulting. An early Ordovician age assignment for the turbiditic deposits resulted from therecent successes of obtaining conodonts from chert interbedded in the greywackes (Stewart, 1988;

7

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in press). The palaeogeographic significance of this new discovery is yet to be determined. Onepossible scenario is that the spreading southward of volcanism which began in the north in theearly Ordovician, elevated the sea-floor so that it was isolated from the northward flowingturbidity currents, which originated from the Antarctic sector of Gondwana.

Figure 3 (after Powell, in Veevers, 1984).

Distribution of Ordovician rocks in south-eastern Australia. A. Early Ordovician. B. Middle and Late Ordovician. Basedon Cas (1983, figs. 7-9), and Powell (1983b). Numbered palaeocurrent sources: 1, Webby (1976, 1978); 2, Schleiger(1968, 1969, 1974); 3, Corbett and Banks (1973); 4, Powell (unpubl. data); 5, Cas et al (1980, appendix 1); 6, Powell andConaghan (unpubl. data); 7, Fergusson (1979); 8, Powell (1983a).

8

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Fig. 4. Present day tectonic elements. Major faults and sutures: (1) Keiwa Fault; (2)Gilmore Fault; (3) Kiandra-Narromine Structure; (4) Long Plain-Indi Fault; (5) Murrum-bidgee Fault; (6) Columbine Thrust; (7) "Bell River" Fault; (8) Copperhannia-Lake GeorgeFault; (9) Deakin Fault; (10) Wiagdon Thrust; (11) Lake Bathurst-Tarago Structure; (12)Eden-Nowra-?Moree Structure; (13) Mt. Wellington Fault; (14) Mt. Ida-McIvor Fault.Smaller subdivisions of the Lachlan Fold Belt: CBT, Cobar Trough; GZ, Girilambone Zone;MHT, Mineral Hill Trough; BGP, Bogan Gate Platform; PP, Parkes Platform; TT, TumutTrough; CT, Cowra Trough; YCZ, Yass-Canberra Zone; MB, Murrumbidgee Basin; BB, BuchanBasin; MH, Molong High; HET, Hill End Trough; MT, Murruin Trough. Names: A, Albury; B,Bathurst; C, Canberra; Co, Cobar; 0, Orange; P, Parkes; SYM, stockyard Mountain 1.

9

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TEXT-FIG. 5. Map showing distribution of Ordovician rocks in central New South Wales. Based onthe 1: 1,000,000 Geological Map of New South Wales (1972).

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10

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As already mentioned, most plate-tectonic reconstructions of the Lachlan Fold Belt of EasternAustralia published in the last two decades, have considered the Ordovician volcanic andsedimentary successions of the volcanic island arc (that is, in the Molong High and the ParkesPlatform of central New South Wales) to lie between the marginal sea (Wagga Trough to the west)and the frontal arc and/or trench to the east (Monaro Trough and equivalents). However therehave been recent, though as yet unsubstantiated interpretations of the volcanic arc being an exoticterrane within the otherwise unbroken, monotonous quartz-rich Ordovician turbidites which areexposed elsewhere in the Lachlan Fold Belt (Fergusson 1991; VandenBerg (1991). In additionWyborn (in press) proposes that the volcanic belts are not the products of true subduction-relatedisland arc volcanism, but represents the delayed partial melting of mantle modified by subductionduring an earlier period of plate convergence. The main pieces of evidence for this proposal are:(a) calcalkaline volcanism is rare, the main products being shoshonitic.(b) the magmatism occurs over a broad area about 400 kilometres across, not the curvilinear beltsexpected in island arc environments.(c) assemblage of Late Precambrian basement blocks by an earlier period of plate convergence ispredicted by the study of granite source-rocks in the Lachlan Fold Belt (Chappell et al., 1988).

In the eastern part of the Molong High, a substantial pile of basic and intermediate volcanics(Walli and Cargo volcanics and their equivalents) was erupted in Early Ordovician times andbecame at least in part emergent, then planated to form the offshore sites for the accumulation ofLate Ordovician carbonates. These shallow-water carbonates formed as terrigenous fringing islandshelf, and terrigenous free bank-type (or mantling) deposits on both eastern (with the CliefdenCaves Limestone Group and equivalents), and western (with the Bowan Park Group andequivalent carbonates) sides of the Molong High (see Fig. 7 for detailed stratigraphicrelationships). The eastern side of the Molong High subsided during the depositional phase of theMalongulli Formation, but became a positive feature again with the influx of Angullong Tuff, andsite for shallow water deposition in the early Silurian. A subaerial trachytic ignimbrite has recentlybeen identified in the Angullong Tuff.

In contrast, the western side of the Molong High remained a positive feature, with shallow-watercarbonates being deposited contemporaneously with the basinal Malongulli Formation, but byearly Silurian times had subsided to become a part of the Cowra Trough.

TEXT-FIG. 6 Diagram showing generalized Ordovician facies interrelationships across MacquarieVolcanic Belt.^ 11

Figure 7 (Based on Stait et al., 1985, and Webby & Percival, 1983).

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12

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13

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Stratigraphic columns of the Cliefden Caves Limestone Group (Upper Ordovician) in the type area nearCliefden Caves. For location of sections I, 2, 3, 4 and 4a see index map

1 4

(ii) Palaeoenvironments of the Upper Ordovician Cliefden Caves and Malongulli successions(volcanic arc shelf and slope):

Day 3 of the excursion will focus on the richly fossil-bearing parts of the Cliefden Cavescarbonate succession on the eastern side of the Molong High (Figs.7-9). The following mainbiofacies types occur in the lower part of the succession, that is, in various repetitions in the FossilHill Limestone (Fig. 10):

(a) The Eodinobolus biofacies, with shell beds (Figsl 1-12), representing protected intertidal toshallow subtidal environments (Webby & Percival (1983).(b) The Tetradium cribriforme biofacies with skeletal lime sands and coral colonies, formed inshoals and bars of a well-aerated moderately high energy zone above wave base.(c) The strophomenide biofacies, characterized by a rich and varied fauna and flora which livedpredominantly on lime muds in an open but quiet subtidal level bottom habitat below wave base.

It is also possible to recognize a rhynchonellide biofacies representing a regressional phase ofdeposition in turbulent near shore conditions (associated with the influx of terrigenous sands), anda quiet, terrigenous free, lagoonal facies The intertonguing and onshore/offshore relationships ofthese main biofacies in the Fossil Hill Limestone is shown in Fig.10.

Much of the overlying massive Belubula Limestone probably also represents similar, terrigenousfree, lagoonal-type depositional conditions.

Stratigraphically higher, in the graptolitic Malongulli Formation, there are important occurrencesof allochthonous limestone breccia which contain not only clasts derived from the shallow-watersof the island shelf, but also tabular blocks of darker grey laminated lime mudstones andwackestones rich in siliceous organisms (sponges, disaggregated spiculaes and radiolarians).These latter seem to represent clasts of more or less consolidated periplatform ooze that waseroded from the floor of the slope as the debris flow traveled basinward. This sponge-radiolarianbiofacies probably before redeposition occupied a location just below the shelf-slope break (Rigby& Webby, 1988).

(iii) Taxonomy and biogeographic significance of volcanic island biotas.

The following papers include taxonomic descriptions and/or discussions about the Ordovicianbiotas from the shelf, and slope associations of the Molong High and Parkes Platform:

Algae (and/or Cyanobacteria) - Semeniuk & Byrnes (1971); Webby (1982); Webby & Trotter(1991)Radiolarians - Webby & Blom (1986)Stromatoporoids. - Etheridge (1895); Webby (1969; 1971a; 1979); Pickett (1970); Webby &Morris (1976).Sponges - Webby (1969); Webby & Morris (1976); Webby & Rigby (1985); Rigby & Webby(1988); Webby & Trotter (in press)^ .Tabulate Corals - Etheridge (1909); Hill (1957); Webby & Semeniuk (1969; 1971) Webby (1977);Webby & Kruse (1984)Rugose Corals - Webby (1971b; 1972a; 1988); McLean & Webby (1976)Bryozoans - Ross (1961)Nautiloids. - Glenister (1952); Stait, Webby & Percival (1985)Brachiopods - Percival (1978, 1979a, 1979b; 1991)Trilobites - Campbell & Durham (1970); Webby (1971b; 1973; 1974); Webby, Moors & McLean(1970)Echinoderms - Webby (1968)Conodonts - Savage (1990)Graptolites - Sherrard (1954; 1962); Moors (1970)Ostracods - Schallreuter (1988); Schallreuter & Siveter (1988a; 1988b; 1988c)

Papers discussing aspects of the biogeographic significance of the faunas include Webby (1974;1985; 1987) and Lin & Webby (1989) - see Fig.13. Aspects of community analysis are consideredby Semeniuk (1973), Webby & Percival (1983) and Webby (1987).

15

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16

(iv) Biostratigraphy

A modern framework for the biostratigraphy of the basinal succession has been established inVictoria using graptolites by Vandenberg (1981) and Cas & Vandenberg (1988). Conodonts arebecoming increasingly important in the basinal facies as techniques for extraction by serialsectioning have developed (Stewart, 1988). The work carried out in Victoria is only now beingapplied in New South Wales.

Biostratigraphic schemes within the central New South Wales volcanic arc successions have beenproposed using the corals and stromatoporoids, the trilobites, and the brachiopods.

(a) Corals and stromatoporoids A workable biostratigraphic scheme has been established by Webby (1969; 1975), Webby et al(1981) and Webby (in Webby & Nicoll, 1989).

C/S Fauna I - typified by abundant labechiid stromatoporoids (notably Cystistroma, Labechiella and Stratodictyon), a varied tabulate component including many species of Tetradiumand the appearance of rugosan Hillophyllum. Best represented in the Fossil Hill Limestone, andof late Gisbornian or early Eastonian age.

C/S Fauna II - characterized by first appearance of clathrodictyid stromatoporoids(Clathrodictyon and Ecclimadictyon), the sphinctozoan Cliefdenella, and rugosan Palaeophyllum,and a most varied and abundant assemblage of heliolitine corals. Well developed in the upper partof the Belubula Limestone and the Vandon Limestone at Cliefden, and in the QuondongLimestone at Bowan Park. It is probably about middle Eastonian age.

C/S Fauna III - typified by first appearances of streptelasmatinid rugosans, Favistina,halysitines and favositids. Best viewed in Bowan Park equivalents on the western side of theMolong High. Also known from shallow-water limestone blocks in the breccias of the MalongulliFormation. Broadly recognized as of late Eastonian to early Bolinclian in age.

C/S Fauna IV - characterized by a rich rugose element (Bowanophyllum,Rhabdelasma and Cyathophylloides) and tabulates (abundant favositids, the first agetolitids,Catenipora and Adaverina). Probably about mid-Bolindian in age, and restricted to top of theMalachi's Hill Beds near Bowan Park.

(b) Trilobites: Four stratigraphically distinct Upper Ordovician trilobite faunules have beenrecognized (Webby, 1974). They are named the Pliomerina prima faunule (approximatelyequivalent to C/S Fauna I), the Pliomerina austrina faunule (approximately equivalent to C/SFauna II), the Malongullia oepiki faunule (which is probably equivalent to the lower half of theC.S Fauna III), and the "Illaenus" incertus faunule(which is equivalent to the topmost part of C/SFauna III).

(c) Brachiopods (contributed by Ian G Percival): Five brachiopod zones are recorded by Percival(1991). The earliest, Fauna A, is distributed through the Fossil Hill Limestone, the AshtonMember of the Regans Creek Limestone, and the Ranch and Bourimbla Limestone members ofthe Daylesford Limestone, Bowan Park Group. Its characteristic assemblage includesEodinobolus, Dinorthis, Plectorthis, Sowerbyites, Wiradjuriella, Anoptambonites, Rhynchotremaand Protozyga; Webbyspira principalis is diagnostic. Fauna AB is present in the lower BelubulaLimestone, and the Gerybong Limestone Member (Daylesford Limestone). This zone is typifiedby abrupt appearance of several new diminutive genera together with rapidly evolving transitionalforms. Fauna B (contemporaneous with coral-stromatoporoid Fauna II) is distributed through theupper Cliefden Caves Limestone Group, the Regans Creek Limestone and the QuondongLimestone (Bowan Park Group). Genera restricted to Fauna B included Eridorthis, Phaceloorthis,

17

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Figure 11 (After Webby & Percival, 1983)

Fig. 11 Stratigraphic distribu-tion of the main faunal andfloral elements of the Glee-sons, Wyoming and basal Ta-plow Limestone Membersbased on the type section atFossil Hill, Cliefden Cavesarea (for location, see Fig.3). Note that approximately30 m of beds are not depictedin the gap between the upperand lower halves of the dia-gram (these beds are howev-er shown in Fig. 3). For keyto symbols used in stratigra-phic column see Fig. 8. Thecircled numerals indi-cate the positions of the insitu shell beds in the Wyo-ming Limestone Member.Approximate relative abun-dance of each faunal and flo-ral element is indicated bythickness of bar on distribu-tion chart. Key to mainfaunal and floral elements asfollows: 1, Eodinobolus; 2,lingulide indet; 3, Rhyncho-trema; 4, Tetradium duplex;5, Tetradium variable; 6, Tet-radium cribriforme; 7, Hullo-phyllum priscum, 8, Bryo-zoa; 9, Pliomerina prima; 10,ostracodes; 11, gastropods;12,echinoderm columnals;13, Hedstroemia (alga).

18

Figure 12 (After Webby & Percival, 1983)

Fig. 12 Schematic representation of Eodinobolus communityshowing two generations of in situ, vertically orientated (umbodownward) articulated shells interspersed with layers of disarti-culated, inclined to horizontally-disposed, shells. Note the rareassociates; algal Hedstroemia at the base, gastropods scatteredthroughout, and Tetradium of the T. variable or tenue type.Ripple-marked substrate is shown at the top of the reconstruc-tion, and an erosional break (disconforrnity) cuts the top of thelower in situ shell bank. Drawn to approximately one quarternatural scale.

19

Figure 13 (After Webby, 1987)

AUSTRALIAN

STAGES

BRITISH

SERIES

EASTERN GONDWANAN CONTINENTAL

SHELF (AUSTRALIAN SECTOR)TASMAMDESUSPECTTERRANES

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Trilobites — with close links to Tasm _SE ASia, China, Korea & Kazakh.(Ptiomerina pros.)

Nautilolds — cosmopolitan longranging only

Brachiopods — with N American &Kazakhstan ties (also 12 of total 43genera endemic)

Stromatoporolds — some species incommon with SE Asia, N China &Kazakh; only genera in commonwith Tasmania

Corals — generic level links withTasmania (Foerstephyllum). Broken R.Embayment (Agetolites), Tamwonh (CyathophylloidesCalapoecia. Halysites). Lesser tieswith Altai, China & N America

Sphinctozoan sponges — links to Alaska,California, N.6, N.W. Chino.

Echinoderm — N American genusAstrocystites^

]-

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Stromatoporolds — also N American links(e.g. Stromatocerium, Aulacera)

Corals — with N American (FoermephynurnII retradium fasmaniense) and centralAsia (Baigolia) ties

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Tremadoc Trilobites with Argent...an hnkS r Cooler waters)

Fig. M. Diagram to show the more significant biogeographic patterns of theOrdovician sequences in eastern Australia, both in the Gondwana continentalmargin and in the Tasmanide suspect terranes.

20

C. ROUTE AND LOCALITY DETAILS

DAY 1: Tuesday 9 July (VVyborn)

The first two days of the excursion will concentrate on examining the quartz-rich greywackebasinal assemblage that is widespread in southern New South Wales and Victoria, and possiblyextends to eastern Tasmania and New Zealand. Figure 14, summarizes the geology of the areacovered on days 1 and 2. There are three main rock group, (1) Ordovician greywacke, overlain by(2) Silurian shallow marine sediments and shallow marine to subaerial felsic volcanics andintruded by (3) extensive areas of granite comagmatic with the felsic volcanics.

The composition of the Ordovician greywackes are monotonously similar almost everywhere,being dominated by quartz detritus in a clay matrix (Wyborn & Chappell, 1982). Feldspar is onlya minor component indicating intensive weathering in the source region and/or several cycles ofsedimentation and erosion. The provenance is from the south and almost certainly involves rocksfrom Antarctica, notably the Robertson Bay Group and Wilson Group in Northern VictoriaLand. Some evidence of an early Ordovician age for the turbidites and late Ordovician age for astarved black graptolitic shale facies, recently recognized further south, both in New South Walesand in Victoria (Glen et al., 1990), will be examined along a well exposed section of greywackewest of Canberra. The section is a man-made exposure along a water pipeline that delivers waterto Canberra from the Cotter River. The section is in a unit known as the Adaminaby Beds.However there has been a proliferation of names for units similar to the Adaminaby Beds thatextend over wide areas of the southern highlands of New South Wales and Victoria, many ofwhich are redundant. Figure 15 shows the distribution of some of the names used locally aroundthe Canberra district.

Before leaving Canberra for the Cotter River we examine a section of Pittman Formation, a unitthat correlates with the Adaminaby Beds, in the northern suburbs of Canberra.

STOP 1: Pittman Formation - Ginninderra Drive

30 minutes

Ref.- Nicholl 1980.

The road section through the upper part of the Pittman Formation shows a transitional faciesbetween turbklite sedimentation and a shaley unit known as the Acton Shale Member. Thickbedded sandstone are exposed at the western end of the section, and grey shale and siltstones tothe east. The shales have yielded the conodont Pygodus serra, which may be seen in handspecimen if you are lucky. Elsewhere graptolites are common in black shales of the Acton ShaleMember higher in the succession.

21

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22

We then proceed out of the suburban parts of Canberra to the west through rolling cleared countryunderlain by an extensive development of Late Silurian felsic volcanics. At the MurrumbidgeeRiver crossing we cross the Murrumbidgee Fault which throws up deeper rocks to the west, thusexposing the Ordovician greywackes intruded by large granitic bodies beneath the felsic volcanics.We travel through the Shannons Flat Granite to the intrusive contact with the Adaminaby Bedson the Bendora Pipeline Road.

Figure 14 Geological Sketchmap of Canberra region.

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23

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7-`71:^Upper OrdovIC fah Lta.Ckr apiel t^sivaies

1-2 Excursion stopS v

— Ordovician l'uripicli#eBe r) etc na Pipeline Road ,

24

STOP 2: Contact of Shannons Flat Granite with Adaminaby Beds 10 minutes.

This stop, and those of the rest of the day, are sketched on Figure 16. Hornfelsing of the sedimentsis well displayed near the contact of the granite, but this particular granite was not particularly hotso the hornfelsing does not extend far into the sediments.

STOP 3: Exposure of a thrust ramp. 10 minutes.

The complexity of the local structure is summarized by this exposure. Gently (25-30°) south-westdipping greywacke is cut by two kink faults with overturned, 50° west dipping, beds between. Themajor Cotter Fault is about 500m to the west of this point, and probably has a similar, west overeast, sense of movement.

Proceed along the pipeline road taking note of the exposures as we go. We will examine some ofthe better sections in detail on our return journey after lunch.

STOP 4: Overturned greywacke sequence with sandstone dyke.

15 minutes

This locality provides us with the first opportunity to examine typical quartz-rich greywackeexposed along the pipeline road. The well-developed graded bedding shows that the sequence isoverturned, and dips 50° west. An unusual sandstone dyke with sharp borders cuts up through thesequence. Any suggestions to its origin would be appreciated.

STOP 5: View of Tidbinbilla Peak

10 minutes

A little further along the road we get a view of the sandstone faces of Tidbinbilla Peak. Theserocks (Tidbinbilla Quartzite) are of Lower Silurian age and form a west-facing dip slope. Thecontact with the underlying Ordovician greywacke is an unconformity with about a 20°discordance. The Tidbinbilla Quartzite is part of a basin developed above the much largerOrdovician basin, after it was first deformed by a fold episode known as the Benambran Orogeny.This deformation mainly affected rocks of the Wagga Trough to the west, and it is suspected thatthe new shelf margin established itself not far west of this point (Owen & Wyborn, 1979). TheTidbinbilla Quartzite was almost certainly derived from the uplifted Wagga Metamorphic Belt tothe west.

25

STOP 6: Picnic lunch on the Cotter River

Exposures of kinked, cleaved black shales are present along the river bank, but access to them maynot be possible if the river is full. No doubt graptolites would be present but the parting is notalong the bedding and no graptolites have been found as yet.

STOP 7: Section through the greywacke sequence

1 hour

At the start of this section there are excellent views down the Cotter River valley, and the route ofthe pipeline can be seen cutting across steep side creeks.

We will walk along a 300m section of greywacke which displays many of the sedimentarystructures present. Grading, convolute bedding, wavey bedding implying a high energyenvironment, load casts, flutes, and amalgamation of turbidite units can be observed. Theamalgamated sandstone units are up to 10m thick. Detritus in the turbidites is quite fine grainedand somewhat bimodal. Larger quartz grains are mostly around lmm across and well rounded, butthe larger proportion of the detritus is 0.3mm or less. Detrital components other than quartz arerare and include: albite, tourmaline, muscovite, zircon, and muscovite-bearing quartzite. Theturbidites have the unusual characteristic of being texturally immature, but compositionallymature. Another thrust ramp similar to stop 3 is exposed part way along the section.

STOP 8: Section through the greywacke up into graptolitic black shales.

1 hour 30 minutes

Another 300 metre section displays the top of the turbidite sequence, which initially is quitesimilar to stop 7. The beds clip and young westward at about 60 0, but an anticlinal axis is crossed,and graded bedding then indicates that the beds dip at a similar attitude to the west, but youngeastwards. We then proceed up section, but down dip. Towards the top of the section cherts appearand sandstones are minor. Conodonts have been observed in the cherts, most easily in muddyinterbeds. The presence of Pygodus anserinus (I. Stewart, pers. comm) indicates a LateDarrawillian to Early Gisbomian age. A few metres above the cherts black shales contain wellpreserved graptolites including (A.H.M. Vandenberg, pers. comm.) Dicellograptus gravis,Dicellograptus sp. (slender), Orthograptus quadrimucronatus, "Climacograptus" tubiferous andAmplixograptus sp. The age is Late Eastonian (Ea4). The difference in age (.15 m.y.) between thecherts and the black shales either implies a very condensed sequence or the presence of beddingparallel thrusts similar to that reported by Glen et al. (1990) from about 100 kilometres to thesouth. Hopefully we will be able to shed some light on this problem on the excursion, as thelocality has not been visited since the age of the chert was determined.

26

Beyond the graptolite locality the road turns sharply back to the north west and back down into thegreywacke sequence. Overturned dip slopes in cuttings beside the road allow us to examine solemarkings on the bases of turbidite beds.

We now return to Canberra, almost back to the Forrest Motor Inn to a cutting close to the newParliament.

STOP 9: State Circle unconformity

20 minutes

Although this stop is not in Ordovician rocks it is a must to see, being so close to the motel. Theexposure, contains Early Silurian State Circle Shale unconformably overlain by Late Silurianshelf facies (Camp Hill Sandstone). The State Circle Shale was probably in the samedepositional basin as the Tidbinbilla Quartzite discussed at Stop 5. The Camp Hill Sandstoneunderlies much of central Canberra, and represents shallow marine deposits that accumulated priorto the outbreak of the widespread Late Silurian volcanism of south eastern Australia, andparticularly the Canberra district.

Overnight at the Forrest Motor Inn. Dinner at the Inn.

27

E4E/41)

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0LE NI LEE. &uê&it y^SKEfett Pi AP AN^S Ee-)CCuRStow STOP 2-1

DAY 2 Wednesday 10 July (VVyborn, Abell and Sherwin) (Fig. 14)

We head north-west along the Barton Highway and turn right just past Gooromon Ponds Creekalong the Bedulluck Road. After 13 kilometres we turn right at a T intersection. A gravel quarry is2.5 kilometres along the road on the left.

STOP 1: Acton Shale Member of the Pittman Formation in Glenlee Quarry (Fig. 17)

45 minute

The Acton Shale Member of the Pittman Formation (Stop 1 of the day before) is well exposedin the area around Picaree Hill, and was once known as the Picaree Formation. The shale is quitesiliceous and pyritic, and above the zone where pyrite has been oxidized forms an ideal road-baseaggregate. The graptolitic fauna is very well preserved in the quarry, though there is somedistortion of the fossils by the cleavage. The site has not yet been studied in detail, but contains(A.H.M. Vandenberg, pers. comm.) Dicellograptus gravis, Dicellograptus sp. (spiralingrhabdosome), "Climacograptus" tubuliferous, Orthograptus quadrimucronatus (s.s.) and 0.pulcherrimus. An age of Late Eastonian (Ea4), similar to Stop 8 yesterday, is indicated, howeverit is probable that a range of ages are present given the quite thick sequence in this area.

We continue east along the road to Gundaroo and take the Collector Road for 3 kilometres. Thestop is across paddocks about lkilometre north of the road.

STOP 2: Pittman Formation with calcareous concretions in Gundaroo Creek G.R. 092240.

45 minutes

Pittman Formation turbidites are unusual from this locality as they contain a high proportion ofcarbonate detritus. The rocks dip 60 0 to the east, but young to the west. The regional metamorphicgrade is upper greenschist facies, and it appears that the metamorphism has mobilized thecarbonate into pods and lenses that continue along strike for many metres. The lenses have aninner white zone containing elongate detrital quartz grains in a matrix of calcite and clinozoisite.The outer green-blue zone contains detrital quartz and original turbidite matrix material, but alsohas small rosettes of actinolite and minor sphene. The origin of the carbonate is problematical, it isunlikely to have come from the volcanic/carbonate belt to the north as there are no volcanicfragments in the turbidites, and conversely there is no source of quartz in that belt. Elsewhere inthe basinal facies carbonate is exceedingly rare.

We retrace our steps to Gundaroo and continue along the Sutton Road to the Federal Highway,and turn left towards Goulburn. On the south-bound lane of the freeway are exposures of PittmanFormation that have been contact metamorphosed by the Late Silurian Sutton Granite

29

STOP 3: Hornfelsed Pittman Formation, Federal Highway.

10 minutes - take care of passing cars.

The Sutton Granite is surrounded by a wide contact aureole in the Pittman Formation.Cordierite spots in the more pelitic fractions of the sequence are aligned in a foliation. The SuttonGranite was intruded just before a widespread deformation in the region, known as the BowningOrogeny. The deformation was not as intense in, and above the granite, as it was elsewhere. Thegranite acted as a somewhat-ridgid block. This area has been used to examine the effects of earlierdeformation than the Bowning Orogeny, and east-west trending folds have been found. These foldsuggest a very different stress field for early deformations compared the dominantly meridionalfolding of the Bowning Orogeny and younger deformations.

It is about 50 minutes drive north to the rural city of Goulburn, where we will take lunch.

We then proceed along the Hume Highway for 10 kilometres towards Sydney.

STOP 4: Old Hume Highway road cutting - Towrang Beds. Late Silurian (Ludlow)graptolites in cleaved siltstone.

20 minutes

Ref. Naylor, 1935, 1938; Pickett 1982.

This is a brief stop to look at Late Silurian lithologies for comparison with those in the LateOrdovician. THe local graptolite fauna includes Monograptus "nilssoni" M. bohemicus and M.dubius.

The contact with the Ordovician strata, about 500m to the east, is a contorted ferruginous zone,probably a fault.

STOP 5: Old Hume Highway cutting - undifferentiated Late Ordovician chert, shale, andsiltstone. 30 minutes

Ref. Naylor, 1935, Offenberg, 1974, Sherrard, 1954.

Graptolites are common in some silty bands in this section, but they are not well preserved andspecific identification is doubtful. Climacograptus bicornis or C. spiniferus is the most distinctiveform present. The cherts and some shales contain radiolaria.

Distance 2 km.

30

STOP 6: Hume Highway cutting - undifferentiated LLandovery sediments with graptolites

30 minutes

Ref. Creaser 1973 (unpubl.)

The lithology at this site is not markedly different from that of some beds at the previous locality,and gives some indication of the difficulty in separating Ordovician and Early Silurian strata inthis region. The graptolites are very abundant on some bedding planes, but the overall thickness ofEarly Silurian strata here is believed restricted to a few metres.

Distance 5km

STOP 7: Hume Highway cutting - undifferentiated Late Ordovician sediments. 30 minutes

Ref. Naylor, 1939; Offenberg, 1974

The lithology at this locality is siltier and less cherty than at Stop 6. The graptolite fauna containspoorly preserved Climacograptus, Dicellograptus and probable Pleurograptus.

Return to Goulburn and towards Yass via Gunning.

STOP 8: Hume Highway cutting - brief stop in the Jerrawa beds to again examineOrdovician quartz-rich turbidites. GR 890446 Gunning 1:100 000.

15 minutes

The greywackes are quite similar to those near Canberra, though a little more weathered. Takegreat care of traffic, very dangerous.

Proceed through Yass and take the Boorowa Road to the right about 10km west of Yass. Thecountry is underlain by the extensive Silurian volcanics that extend north from Canberra. Somevery large ignimbritic eruptions took place, extending meridionally for up to 80 km, with up to10003km of erupted products in a single cooling unit. In the immediate area around Yass thefamous latest Silurian Yass basin contains a rich shallow marine fauna. The Yass basin overliesthe Silurian volcanics, but is in turn overlain by early Devonian volcanics.

On the northern outskirts of Boorowa we turn right, and along the Kenyu Road for 26 km.

31

STOP 9: Kenyu Formation, first stop in the Ordovician volcaniclastic fades. GR 631137Boorowa 1:100 000 sheet

20minutes

The Silurian volcanics that have dominated the countryside from east of Yass, and which furtherwest continue north for another 80 km, are here underlain, not by quartz-rich greywacke, but bypartly silicified feldspathic tuffs. Volcanic bombs of a plagioclase-phyric "andesite" up to 20cmacross are present in the tuffs. The Kenyu Formation can be traced north into the Walli"Andesite" north of Cowra, an area where we will be visiting the next day.

Continue north to Cowra, overnight in the Cowra Motor Inn. Dinner at the Motor Inn.

Cowra is built mainly on the south bank of the Lachlan River, at about 305 m above sea level, andis overlooked by hills of the Silurian S-type Cowra Granodiorite - the name is local Aboriginal for"The Rocks". The town was settled in 1833, and has become a centre for the local farming district,with a population now over 11,000. During World War 11, a prisoner-of-war camp was establishedon its outskirts, and eventually housed several thousand inmates, mainly Italian and Japanese. On5 August 1944, 1,104 Japanese prisoners attempted to escape, and in the ensuing action 4Australian soldiers and 231 Japanese died. A Japanese War Cemetery has become the focus ofstrong emotional ties with Japan, which have been augmented by a Japanese Cultural Centre withextensive Japanese Garden.

32

DAY THREE: Thursday 11 July (Webby)

Today will be spent examining the Ordovician succession in the Cliefden Caves area (eastern partof the Molong High), including the ?Lower Ordovician Walli Andesite, the Upper OrdovicianCliefden Caves Limestone Group (especially the lower and upper, fossiliferous, thin-beddedsubdivisions of the group, namely the Fossil Hill Limestone and the Vandon Limestone. Thesucceeding Malongulli Formation will also be studied.

We leave Cowra at 0815, heading east along the Mid-Western Highway. The hills immediately tothe north (left) as we leave town are the Cowra Granodiorite. Beyond the town the highway ismainly on the alluvial flats of Waugoola Creek, flanked to the north by low hills of Silurian shalesand felsic volcanics (the Canowindra Porphyry). We take a minor road to the left 22 km fromCowra, heading north towards Walli. This minor road runs approximately along the line of theColumbine Mountain Thrust, a major structural break separating Cowra Trough Silurian shales,silicic volcanics and local limestones (such as the Liscombe Pools Limestone immediately east ofthe Cliefden Caves area) from the eastern part of the Molong High with its Ordovician "andesitic"volcanic - limestone - shale belt (from lower to upper succession of Walli, Cliefden Caves, andMalongulli units, succeeded by the Angullong Tuff.At 28 km we join the Canowindra-Mandurama road, and head to the east. You will note a fewscattered, mainly weathered outcrops of Walli "Andesite" and one of massive Cliefden Caveslimestones along the roadside. At 34.5 km we turn off the Canowindra-Mandurama road to headnorthwards into the Cliefden Caves area.

STOP 1: Pillow lavas in basalts of the Walli "Andesite", Limestone Creek.

Our first stop is on Limestone Creek, to examine the pillow lavas in the ?Lower Ordovician Wall"Andesite" formerly studied by Smith (196 1968).

We next proceed past excellent exposures of the massive middle part of the Cliefden CavesLimestone Group (the Belubula Limestone) near "Wyoming" homestead, cross LimestoneCreek, and continue past the homesteads of "Malongulli" and "Boonderoo" to the top of the ridge,near the silo on the Caves track, with excellent views of the Belubula Valley (Stop 2). TheBelubula River is a west flowing tributary of the Lachlan. We are now 40 km from Cowra.

STOP 2: Overview of Topography and Local Geology (Fig.7-9):

This stop, just before we descend into the Belubula Valley to study the important fossiliferoussections in the Fossil Hill Limestone on Fossil Hill and on Dunhill Bluff, gives a view of theregional topography, and opportunity to consider the general geology, the local stratigraphicsuccession, and regional correlations.

33

To the north the Miocene volcanic pile of Mount Canobolas (1,395m) stands above a prominent"peneplain" surface. The Belubula River has cut its present valley as an antecedent oranteconsequent stream over about 12 million years. The most deeply incised gorge (the sag in theskyline ridge to the west) is at The Needles, where the river cuts through resistant N-S trending,W-dipping, non-marine Upper Devonian quartzite and sandstone. Farther south is the conicalMalongulli Sugarloaf (644 m), again capped by Upper Devonian sandstones which restunconformably on the Upper Ordovician Angullong Tuff.

In terms of local geology (Webby & Packham, 1982), we are standing on the nose of a gentlynorth-plunging anticline. Massive resistant Lower Ordovician Walli "Andesite" forming theridge is overlain, down-slope to east, north and west, by less resistant limestones (Cliefden Cavessuccession) and succeeding siltstones and shales (Malongulli Formation). The more resistantUpper Ordovician Angullong Tuff forms the hills to the east, the slopes below the peneplainsurface to the north, and the hills below the ridge-forming Devonian sandstones to the west.

STOP 3: Fossil Hill, Belubula River. Contact with Walli Andesite, and examination andcollecting from the Gleesons, Kalimna, Wyoming and Taplow Members of the overlyingFossils Hill Limestone (Upper Ordovician).

To reach this locality at the contact between the top of the Walli Andesite and the base of theFossil Hill Limestone we will drive down the valley past a disused barytes mine in the topmostWalli Andesite, to the Large Flat, and then walk a short distance on to Fossil Hill. If it rains wemay be forced to walk a considerably longer distance - just over a kilometre - from the ridge top!

(a) The first fossils occur in the "lithic" unit of the Gleesons Limestone Member,about 2 m above the base of the member (Figs.10-11). They include rare gastropods, brachiopods,the trilobite Pliomerina and ostracods. About 0.5m above the ten in situ Eodinobolus shell beds ofthe Gleesons Limestone Member we will see occurrences of the 0.2m thick Tetradium variabilecoral thicket, directly overlying algal Hedstroemia mats. This coral association is seemingly a partof the low-diversity Eodinobolus facies (Fig,12), which has been interpreted as having formed in aprotected, muddy, intertidal to shallow subtidal environment (Webby & Percival 1983). Thecolonies of T. variabile have a similar growth form to T. cellulosum "super colonies" of theMiddle Ordovician Black River Group, eastern North America (Walker 1972), but do not seemto have formed in the same moderate- to high-energy subtidal wave-baffle community as Walkerhas depicted for the T. cellulosum colonies. Similar associations occur in the lower part of theBowan Park and Regan's Creek Limestone successions, but with a greater variety of species ofTetradium (T. apertum, T. bowanense and T. compactum), and with the addition of the cylindricalstromatoporoid Alleynodictyon. This association has been suggested as developing in a quiet,protected area of the shallow platform, perhaps towards the outer edge of a lagoon.

(b) The succeeding Kalimna Limestone Member on Fossil Hill (Fig. 10) comprises a

34

sequence of well bedded skeletal wackestones and packstones with silty interbeds, passing up intoa distinctive 1.2m thick coral-algal-stromatoporoid biostrome dominated (up to 95% of thebiovolume) by massive "heads" of Tetradium cribriforme, up to 500 mm across and 300 mm high.Minor constituents of the biostrome include the stromatoporoid Cystistroma donnellii, the tabulatecorals Nyctopora, Coccoseris, Eofletcheria and Bajgolia, the rugosan Hillophyllum., bryozoanBatostoma, and brachiopod Rhynchotrema. Similar occurrences of corals and stromatoporoidsmay be found on bedding planes through the sequence immediately below the biostrome, and upthrough part of the overlying Wyoming Limestone Member. These beds belong to theTetradium cribriforme facies, and the biostrome in particular reflects a moderately active, wellaerated depositional environment. Bryozoans (especially Batostoma), and trilobites(Eokosovopeltis atavus Pseudobasilicus? fortis Remopleurides acer and Pliomerina prima) arealso reasonably common in the sequence below the biostrome.

(c) Wyoming Limestone Member. A rich and varied fauna is represented in thelower part of the section, 4-5 m above the base, with the brachiopods Dinorthis Sowerbyites,Webbyspira and Rhynchotrema, the trilobites Pseudobasilicus? and Remopleurides, the coralsBajgolia, Nyctopora and Hillophyllum, and the bryozoan Batostroma. Higher there are severalterrigenous influxes, with Rhynchotrema the most common brachiopod in these coarser sandydeposits. In the upper part of this lithic-dominated Member there is an upward shallowing of faciesback to the distinctive Eodinobolus shell beds (Fig. 11). This is followed by deepening again intothe overlying Taplow Limestone Member, with its massively bedded calcarenites (packstones)containing large boulder like colonies of Tetradium cribriforme suggesting some sort of active,high-energy shoal-type deposit, near or above wave base. This same Wyoming/Taplow contactwill be noted at the next stop, on Dunhill Bluff.

STOP 4: Dunhill Bluff, Belubula River. Study of Taplow to Dunhill Bluff Members of theFossil Hill Limestone.

The Dunhill Bluff section is immediately northeast of Fossil Hill, and is the type section for theupper half of the Fossil Hill Limestone (Fig.8).

T. cribriforme unit defines the base of the Taplow Limestone Member and a massively beddedskeletal packstone and grainstone with clasts of mainly algal, echinoderm and bryozoan derivationfollows. This grades upwards into thinner bedded wackestones and lime mudstones with a fewshaly partings, and a fauna of brachiopods (Wiradjuriella, Sowerbyites and Plectorthis), trilobites(Pseudobasilicus?), gastropods, and nautiloids. Then with more shaly partings, this grades into themore offshore, richly fossiliferous, level-bottom Dunhill Bluff Limestone Member (Fig. 10). Thethin-bedded, alternating skeletal packstone, wackestone and calcareous siltstone show a mixedfauna of brachiopods (Sowerbvites, Wiradjuriella, Rhynchotrema, Plectorthis andAnoptambonites), the trilobites Pseudobasilicus? and Eokosovopeltis, gastropods, bryozoans,algae, and a few small corals (Nyctopora and Bajgolia).

35

Higher in the Dunhill Bluff Limestone Member, and probably accompanying another shallowingevent, there is an increase in abundance and diversity of corals, even some very small bioherm-like developments, with associated T. cribriforme, T. cruciforme Eofletcheria hadra Nyctopora,Bajgolia, the rugosan Hillophyllum priscum, and the stromatoporoids Rosenella woyuensis,Cystistroma donnellii and Labechiella regularis. There are larger biohermal masses elsewhere atthis stratigraphic level (see the next stop).

The uppermost part of the Fossil Hill Limestone (the Transmission Limestone Member) and themassively bedded 290 m thick Belubula Limestone will not be examined, not only throughshortage of time but because few horizons have well preserved, easily extracted, biotas. Onehorizon towards the middle of the Belubula Limestone is worthy of comment even though itcannot be visited. It is best known from the Licking Hole Creek area west of Cliefden Caves.Named the "E Horizon" by Percival (1976), it contains a distinctive association of theclathrodictyid stromatoporoid Ecclimadictyon nestori, and Eofletcheria-like tabulate and cf.Eodinobolus. This level marks the first appearance of clathroclictyids in the Ordovician sequence,and defines the base of the biostratigraphically distinct coral-stromatoporoid Fauna II of Webby(1969); Webby et al. (1981) and Webby & Nicoll (1989).STOP 5: West Boonderoo Shearing Shed - 'reefal' facies in the Dunhill Bluff Member of theFossil Hill Limestone.

This will be a fairly brief collecting stop at a large biohermal mass in the Dunhill BluffLimestone Member. The fauna recorded from here includes the stromatoporoids Cystistromadonnellii Labechiella regularis, Stratodictyon columnare, Pseudostylodictyon aff. poshanense andan unnamed cylindrical form, and the corals Hillophyllum priscum, Tetradium cribriforme, T.cruciforme, Eofletcheria hadra Bajgolia caespitosa, Nyctopora sp. Coccoseris sp. and otherheliolitines.

Picnic lunch, west bank of the Belubula River; at its confluence with Coppermine Creek, whichis the next locality to be visited.

STOP 6: Coppermine Creek at confluence with the Belubula River - lower part of theMalongulli Formation (Upper Ordovician)

A prominent cliff-forming limestone breccia deposit overlies the thin-bedded dark grey graptoliticshales and siltstones of the lower Malongulli Formation at the confluence of Coppermine Creekwith the Belubula River. Moors (1970) identified the graptolites as including Leptograptuseastonensis, Climacograptus tubiferus Dicellograptus elegans and Dicranograptus cf. hians kirki,which in the revised Australian biostratigraphic scheme of VandenBerg (in Webby et al., 1981)may be assigned to the Eastonian (Ea3) Zone of D. hians kirki, (i.e., about Late Caradoc in age).

36

Figure 18 (After Rigby & Webby,1988)

Cop- Lower UpperSugar- per-^Glee- Glee-loaf mine sons^sons

Creek Creek Creek CreekSponge taxa 1 2 3a 3b

Demospongea:Hapfission regularis - +Warrigalia elliptica -Warrigalia robusta - +Taplowia ordinata - +Lewinia cavernosa + +Lewinia complanata - +Boonderooia spiculata - +Cliefdenospongia lamina . - +Archaeoscyphia minganensis - + -Aulocopium aurantium + + + -

Perissocoelid habra + + + +Hudsonospongia cf. H. cydostoma - - +Patellispongia australis - + -Psarodictyum crassum - +Amplaspongia bulba - +Amplaspongia magnipora - + -Malongullospongia delicatula - - +Pseudopalmatohindia digitata - + -Dunhillia tubula - +Dunhillia a. pertura - +Dunhillia cribrata - +Dunhillia multiporata - +Yarrowigahia brassicata + - -

Gleesonia porosa + +Vandonia dathrata + - -

Hindia sphaeroidalis + + +Belubulaspongia gigantea - +Palmatokindia multipora + +Palmatohindia cylindrica - +Palmatohindia (?)favosa - +Arborohindia uniforma - +Arborohindia parva - +Mamelohindia planata - +Fenestrospongia explanata - + -

Astylostroma micra + - +Hexactinellida:

Tiddalickia quadrata +Wongaspongia minor + _Won gaspongia major + +Walliospongia grad/is - - +Liscombispongia nodosa - +Wareembaia concentrica - +Kalimnospongia pert usa - +root tuft - +

Calcarea:Nibiconia adnata +Belubulaia packhami (?) +

Table^Distribution of sponges inthe Malongulli Formation, New SouthWales; + = present, - = absent.

37

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Figure 19 (After Webby Packham, 1982)

Stratigraphic column of upper part of the Belubula Limestone and the Vandon Limestone at TrilobiteHill (section 5; for location see Figure 3) showing the distribution of fossils. This is the type section forthe Trilobite Hill Limestone Member of the Vandon Limestone. Note the disconformable contact betweenthe Vandon Limestone and the overlying Malongulli Formation.

38

The limestone breccia is up to 8m thick, and shows a regular outcrop on the cliffs but is somewhatcomplexly folded and faulted in this surface expression above those cliffs. The deposit is poorlysorted and shows a crude upward grading from clasts up to 450 mm across. The clasts are of twotypes: elongate tabular blocks of dark grey laminated spiculitic lime mudstone and wackestone,and massive-rounded light grey coralline wackestones and packstones. The rugosan Favistina,heliolitines and favositids are the most common coral types in these "shallow-water"allochthonous clasts, and there is an extraordinarily rich siliceous sponge fauna (some 28 speciesof lithistids and 5 of hexactinellids, including 19 new genera, 29 new species) in the elongate,tabular "deeper-water" clasts (see Fig. 18). The commonest are species of the spherical Hindiaand the stick-like Dunhillia. The assemblage in this Coppermine Creek locality was described byRigby & Webby (1988). Only three species, of Archaeoscyphia, Aulocopodium and Hindia, areallied to species previously described in North America and Europe. There is also a diverseradiolarian association in these "deeper-water" clasts (Webby & Blom 1986).

The limestone clasts containing the sponges and radiolarians appear to have been derived frompen-platform oozes of the "deeper-water" slope facies as debris flows moved basinward. Thesiliceous sponges seem to have thrived in a "deeper-water" island slope habitat, possibly in an areaof equatorial divergence where upwelling was contributing significant quantities of silica. Thelimestone breccias also contain "shallow-water" clasts with corals (Favistina) and other elementswhich are representative of Fauna III. This material was derived from contemporaneouslyforming bank deposits, probably from the upper part of the Bowan Park Limestone and itscontemporaries to the west.

STOP 7: Trilobite Hill, Belubula River - succession through the upper Belubula Limestone,Vandon Limestone and the basal Malongulli Formation (Upper Ordovician).

It is a short walk along the south side of the Belubula River to Trilobite Hill - the name derivesfrom Opik's 1951 discovery of trilobites in the basal calcareous spiculitic siltstones of theMalongulli Formation, which caps the hilltop (Fig. 19). The main cliff-forming part of the sectionexposes the upper part of the Belubula Limestone, which is succeeded by the VandonLimestone. This is divided into a lower, thinly bedded 22m thick Trilobite Hill LimestoneMember, and an upper massive, burrow-mottled, 1.5m thick Mt. Lewin Limestone Member.The middle and upper parts of the Trilobite Hill Limestone Member exhibit abundant heliolitinecorals, Tetradium cribriforme, clathrodictyids (Ecclimadictvon, Clathrodictyon) and brachiopodAustralispira. The rugosan Palaeophyllum proliferum has also been found in the uppermost part.The trilobites, graptolities and brachiopods of the overlying basal Malongulli Formation havebeen documented by Webby et al. (1970), Webby (1973; 1974), Moors (1970) and Percival(1979a, 1979b).

Return to Cowra, overnight at the Cowra Motor Inn. Dinner at the Quarry Restaurant at CowraWinery 4km south of Cowra on the Boorowa Road.

39

DAY 4 Friday 12 July (Wyborn and Sherwin)

Today we continue in the volcanic and volcaniclastic sequences of the Orange and Molongregions.

From Cowra proceed NE along the Mid Western Highway to Mandurama, and turn right on theGallymont Road. At 3km the main road to Gallymont bends left, but we continue straight ahead toNuneham Park.

STOP 1: Quartz-rich sediments of the Abecrombie Beds (basinal sequence) prior to thebreaking out of volcanism.

15 minutes

We have traveled south from Mandurama to the northern end of the Silurian Wyangala Batholith.A narrow belt of Abecrombie Beds wraps around the northern end of the batholith. All beddingdirections young to the north, but in the aureole of the batholith there are two deformations. Thefirst is probably related to forceful emplacement of the pluton in this area, known as the GarlandGranodiorite. The second imparts a meridional cleavage on the sediments, which extendsnorthwards into the overlying volcaniclastic sequence, and weakens. This deformation alsodevelops a weak foliation on the ganodiorite, but plutons further south, of much the same age, arestrongly foliated. The age of this post-granite deformation is probably mid Devonian, and knownas the Tabberaberan Orogeny.

The composition of the Abecrombie Beds is indistinguishable from the quartz-rich greywackesedimentation we have already examined near Canberra and Goulburn. At this outcrop, quartz hasbeen mobilized into abundant quartz veins parallel to the DI cleavage and the GarlandGranodiorite contact. D2 has produced some spectacular steeply north-plunging folds of Flcleavage, which is roughly parallel to bedding.

Return to the Gallymont Road junction, and turn left through some historical entrance gates intothe Rockville property, and continue down to Mandurama Ponds Creek.

STOP 2: Volcaniclastic sediments of the Rockville Formation (new name) below the MountPleasant Basalt.

30 minutes

The excellent outcrops in Mandurama Ponds Creek consist of feldspathic turbidite, greentuffaceous siltstones and tuffaceous chert. Some of the turbidite beds are over lm thick, and quitecoarse grained at their bases. Albite and altered volcanic rock fragments are the dominant detrital

40

component, but a little quartz (<5%) is present in some beds. This is in stark contrast to Stop 1.The beds dip and young to the north-east, and the F2 cleavage, of Stop 1 is still quite strong. Themetamorphic grade is lower greenschist facies. Further north cleavage is only weakly developedand metamorphism decreases to prehnite grade.

Return to Mandurama and turn left on the Highway for 200m, and then right on the Junction Reefsroad. Dark grey mudstones with feldspathic siltstone dominate the sequence, but the higher hills tothe north mark an increase in volcanism with first coarse volcaniclastic sandstones andconglomerates, followed by the pillow lavas of the Mount Pleasant Basalt.

STOP 3: Mount Pleasant Basalt, pillow lavas at Montana property.

20 minutes

The Mount Pleasant Basalt is a distinctive marker unit in the volcaniclastic sequence of theMandurama - Junction Reefs area. The stratigraphic nomenclature in the area needs clarification,as the rocks above the Mount Pleasant Basalt were originally correlated with the UpperOrdovician Malongulli Formation (Stops 6 and 7, yesterday). However specimens of graptoliteGlyptograptus teretiusculus and the trilobite Shumardia have been recorded previously suggestinga Darriwilian age (Stevens,1957; Webby 1973). The Mount Pleasant Basalt has been consideredto have a pre-Darriwilian age, and to be correlative with the Walli Andesite (Smith 1966). Thebasalt is quite porphyritic with about 40% phenocrysts of albitized plagioclase, clinopyroxene andaltered olivine. The pillows are quite large, over 2m across, and only recognizable as pillows whenwell exposed. Perhaps the large size of the pillows is related to a higher viscosity resulting fromthe crystal rich nature of the lava. The chemical composition is typically shoshonitic, and wouldclassify as a potassic trachybasalt using the recommended IUGS scheme (Le Bas et al., 1986). Anattempt to separate zircons from the rock for ion probe dating was made from this locality, butwithout success.

Continue along the road to Junction Reefs to visit the Sheehan-Grants Gold Mine

STOP 4: Sheehan-Grants Gold Mine at Junction Reefs

lhour

The mine, jointly owned by Climax Mining and Arimco NL, is thought to be part of a hightemperature skarn system emanating from an Ordovician shoshonitic intrusion, known as theJunction Reefs Monzodiorite. The mineralization is in a series of calcareous beds known as orebeds, that have been metasomatized to calcsilicates and containing about 4g/ton gold. Severalother deposits have also been proven up in the area, all about the same distance away from theJunction Reefs Monzocliorite. Closer to the intrusion the skarn is higher temperature, but lacks

41

gold. Total reserves are in the order of 2.5 million tons at 3 g/ton. The calcsilicate beds areseparated by mudstones and volcaniclastic siltstones in a sequence which also contains coarsevolcaniclastic sandstones and, higher up, matrix supported volcanic conglomerates. Theconglomerates are overlain by pyroxene-rich basalts, breccias and a trachytic unit that appears tobe a subaerial ignimbrite. Chemical analyses indicate all igneous rocks, including the intrusionscan be related by fractional crystallization, though there appears to be two separate ages ofmagmatism. Hornblende-bearing dykes of Mount Pleasant Basalt age have been dated (Perkins etal., 1990)by the Ar/Ar technique at 479±2ma (Early Darriwilian?), but the Junction ReefsMonzodiorite, the nearby much larger Prince of Wales Monzodimite, and possibly the volcanicunits above the conglomerates are Late Ordovician. The two monzodiorites have been dated at 440ma. Zircons have been separated from the trachytic unit, but they have not been ion probed yet.Evidence from here and elsewhere, particularly the Parkes area (days 5 and 6), indicate that theOrdovician magmatism is of major economic importance (Wyborn, 1988, 1990, in press;Hiethersay et al, 1990).

Provided the Belubula River is not in high flow we can continue past the mine towards BurntYard, or else a detour back through Mandurama might be necessary.

STOP 5 Volcanogenic conglomerate or lapilli tuff

15 minutes

As we travel north we continue up sequence, and are now near the top of the matrix supportedconglomerate. Here the conglomerate is fine grained and contains tuffaceous chert fragments anddistinctive volcanic rock fragments with phenocrysts of elongate hornblende needles.

The route continues north, up onto the Tertiary basalt flood plain to the east of the MountCanobolas central volcano, and on into the city of Orange (population 35000).

Lunch in Orange.

1400 depart Orange

distance 20 km, time interval 20 min.

STOP 6. Keenan's quarry - Cheesemans Creek Formation. Late Ordovician (Eastonian)graptolites and rare trilobites in siltstone interbedded with volcanogenic sandstone.

one hour

Ref.- Sherwin 1971.

42

Exposure in this quarry will depend upon the state in which it was left after the last load of gravelwas removed. However it should be possible to examine blocks of massive sandstone derivedfrom nearby andesitic volcanics and the south wall consists of graptolitic siltstones.

The volcanics in this formation are mostly feldspar - pyroxene porphyries with a very fine orglassy groundmass. The feldspars have been altered to albite, with minor replacement bycarbonate and clay minerals

The siltstones are siliceous with some carbonaceous matter and typical of those interbedded withintermediate to basic volcanic sequences in central western New South Wales. The graptolites areflattened and carbonised but otherwise well preserved, and are most abundant at the south end ofthe quarry. The fauna indicates a Gisbornian - Eastonian age but a revision is desirable, especiallywith respect to the diplograptids. The following species were listed for the lower part (being thatpart here exposed) of the Cheesemans Creek Formation by Sherwin (1979) - Climacograptus bicornis tridentatus, Dicellograptus cf. intortus D. cf. morrisi fE D. alector), Leptograptus flaccidus (= L. capillaris) and Orthograptus cf. apiculatus.

Webby (1974) has described the trilobite Triardrus from this locality.

distance 23 km, time interval 20 min.

The road from Orange to Quondong passes over Ordovician and Silurian volcanics and sediments.The escarpments at the top of the hills for six kilometres past stop 5 are Miocene basalts. Theprominent ridge on the right just past the Molong turnoff is formed by Late Devonian fluvialsandstones.

STOP 7 Quondong - Bowan Park Group. Silicified Late Ordovician shelly faunas. IncludesPaling Yards section. (I. Percival, L. Sherwin).

one hour

Ref.- Percival 1980, Semeniuk 1970.

The Bowan Park Group (Semeniuk 1970, 1973a), 560 m thick, consists of (in ascendingstratigraphic order) the Daylesford Limestone, Quondong Limestone and BallingooleLimestone (figs 8, 9). The Daylesford and Ballingoole Limestones are subdivided on the basisof lithological and palaeontological characteristics (Semeniuk 1973a) into a number of members,separated by minor disconformities.

The Ranch Member is the basal subdivision of the 250 m thick Daylesford Limestone, and

43

disconformably overlies the Early - Middle Ordovician Cargo Andesite. Three units arerecognised in this member (Semeniuk 1973b). The lowermost 3.6 m of the dominantly clasticUnit I consists of coarse lithic sandstone containing abundant specimens of Rhynchotrema oepiki together with rare lingulides (Stevens 1957). The latter persist through succeeding mudstones tothe top of Unit 1. Occasional specimens of Rhynchotrema sp., with rare Dinorthis sp. andWebbyspira sp. occur in interbedded grainstone, packstone, wackestone, and lime mudstone of theoverlying Unit 2. The next appearance of brachiopods in the sequence is in shell beds of theBourimbla Limestone Member (fig. 9), where Protozyga is a minor constituent of the distinctiveEodinobolus - Tetradium - Alleynodictyon assemblage (Semeniuk 1971, 1973b). No brachiopodswere recovered from the superadjacent Manooka Limestone Member, although Semeniuk(1973a) recognised Protozyga, Australispira and Wiradjuriella in thin sections of lithologies fromthis member. The succeeding Gerybong Limestone Member, however, contains a relativelyprolific molluscan and brachiopod fauna recovered from silicified residues. Species present arepredominantly of diminutive size and include Protozyga, Zygospira, Australispira, Didymelasma,Quondongia, Bowanorthis and Paraonychoplecia. Brachiopods are generally of rare occurrence inthe Oakley Limestone Member, interpreted by Semeniuk (1973b) as a shallow water faciesequivalent of the Manooka and Gerybong Limestone Members, and are not known from thesucceeding Glenrae Limestone Member. Protozyga is occasionally observed in thin sectionsfrom the Davys Plains Limestone Member, the uppermost subdivision of the DaylesfordLimestone (Semeniuk 1973b, fig. 15).

The Quondong Limestone, 34 m thick, disconformably overlies the Daylesford Limestone.Like its correlative, the Vandon Limestone (Trilobite Hill Limestone Member) of the CliefdenCaves Group, this formation is extremely fossiliferous with a diverse fauna, predominantlyheliolitid corals, brachiopods, molluscs and bryozoa. Brachiopod genera include Wiradjuriella,Hesperorthis, Ptychopleurella, Eridorthis, Phaceloorthis, Zygospira, Australispira, Bowanorthis,Sowerbyites, Trigrammaria, Tylambonites, Quondongia, Molongcola, Doleroides, Skenidioidesand Christiania. These finely silicified fossils occur in skeletal grainstones.

Indeterminate, poorly preserved pentamerides are the only brachiopods known from theconformably overlying Ballingoole Limestone of Fauna Ill age. Similar unidentified pentameridesalso occur in the upper part of the Cargo Creek Limestone, 17 km to the south of Bowan Park,which is comparable in age with the Ballingoole Limestone (Webby & Morris 1976).

distance 77 km, time interval 50 min.

Between Cudal and Manildra there is an excellent view east to Mt Canobolas which at this timeshould be lit by the setting sun.

Overnight at Court Street motel Parkes, ph. 068 623844

44

Day 5 Saturday 13 July. .

distance 14 km, time interval 15 min.

STOP 1. Yarrimbah, north west of Parkes - Yarrimbah Chert. Early Ordovician(Lancefieldian - Bendigonian) siltstones and cherts with graptolites and brachiopods associatedwith shoshonitic volcanics. (L. Sherwin)

one hour

Ref.- Krynen et al., 1990.

The dominant lithology is chert, especially in the gravel pit on the crest of the rise, although muchof the silicification may be secondary. The conglomerate at the base of the Yarrimbah Chertcontains poorly rounded cobbles and pebbles of underlying volcanic rocks in a volcanogenicsandy matrix. There is a thin limestone downslope of the gravel pit. The upper part of theformation, perhaps as much as a third of the total thickness, consists of coarse to medium volcanicsandstone which grades into quartzose siltstone resembling that in the much younger CottonFormation.

At this locality the graptolites Eotetragraptus quadribrachiatus, E. approximatus and Tetragraptuscf. serra have been collected. Elsewhere in the Yarrimbah Chert Paradelograptus pritchardi hasbeen recorded. (Identifications by B.D. Erdtmann and L. Sherwin).

distance 23 km, time interval 25 min

STOP 2. Currajong Park - Goonumbla Volcanics - Gunningbland Shale Member. LateOrdovician brachiopods in siltstone. (I. Percival and L. Sherwin).

one hour

Ref.- Sherwin 1973, Percival 1978 and Krynen et al., 1990.

The Gunningbland Shale Member includes the shale and minor volcanic conglomerate,tuffaceous sandstone and limestone outcrops and abundant float around Gunningbland.Graptolites found elsewhere in the Gunningbland Shale Member indicate an Eastonian age. Thelocality at Currajong Park overlies limestone containing corals and stromatoporoids indicative of aFauna III age in the local biostratigraphic scheme established by Webby (1969). Percival (1978,1979a, 1979b) has described the palaeoecological significance of the brachiopod faunas in theGunningbland Shale Member and from this locality described Casquella bifida Elliptoglossasp., Kassinella anisa ?Dulankarella partita, Sowerbyites vesciseptus, Gunningblandella resupinata,

45

Doleroides sp., ?Scaphorthis aulacis, Wiradjuriella sp., Sowerbyella anticipata, ?Oepikina sp. andInfurca tessellata.

Also present is a diverse, undescribed trilobite fauna comprising Remopleurides sp.,Eokosovopeltis sp., Illaenus (Parillaenus)? sp., Pseudobasilicus sp., Amphilichas sp.,Encrinuraspis sp., aff. Bevanopsis sp., harpids and odontopleurids (Webby, pers. comm.).

distance 5 km, time interval 5 min

STOP 3. New Durran - Goonumbla Volcanics - Gunningbland Shale Member. (I. Percivaland L.Sherwin).

one hour

Ref.- Sherwin 1973 with some assistance on graptolite identifications by J. Riva.

This locality is approximately the same age as the last but there is a greater variety of rock typespresent, including shoshonitic volcanics, coarse volcanic conglomerates, fine feldspathicsandstone, shale and limestone. The limestone is more abundant near the house, the othersediments being best exposed in scrapes down the slope to the west. Fossiliferous float isscattered throughout the ploughed paddock to the north.

Campbell and Durham (1970) described the trilobite Parkesolithus gradyi from this locality anddisarticulated specimens are still reasonably abundant despite repeated collecting trips. Thegraptolite fauna includes Dictyonema sp., Dicranograptus cf. tealei (= D. hians subsp.),Orthograptus quadrimucronatus micracanthus, 0. amplexicaulis, 0. calcaratus subsp., andClimacograptus crassitestus. Percival (1978, 1979a) has recorded Anomaloglossa porca, Paterulasp., Elliptoglossa adela Durranella septata and Sowerbyella (Sowerbyella) lepta. Tetradium sp isthe most common tabulate coral in the limestone.

distance 6.5 km, time interval 5 min.

STOP 4 Nelungaloo - Goonumbla Volcanics - Billabong Creek Limestone Member. Corals,stromatoporoids, silicified brachiopods and ostracodes, conodonts. (B.D. Webby, I. Percival,L.Sherwin)

one hour

This locality consists of a series of scattered outcrops south to Billabong Creek.Ref.- Krynen et al., 1990

46

The Billabong Creek Limestone Member varies from marl to oolitic limestone, although thelatter lithology has been found only as float at the base of the member. The lower part is mostlyreddish in colour, pisolitic in places, with a high fossil content of corals and gastropods. Theupper part is much less fossiliferous with more terrigenous matter and a grey to yellow colour.

This unit has been dated by brachiopods and conodonts (Packham 1967), corals andstromatoporoids (Webby 1976; Pickett 1985) and trilobites (Webby 1971, 1973). The age rangesfrom near the Gisbornian - Eastonian boundary to mid Eastonian, or Fauna I-11 (Pickett 1985).The brachiopod fauna, described (Percival 1991, comprises Wiradiuriella halis Sowerbyitesisotes Doleroides mixticius Australispira disticha Rhynchotrema oepiki, Eridorthis australisSowerbyella billabongensis, Protozyga definitiva, Zygospira carinata Bowanorthis fragilis,Paraonychoplecia inversa and Didymelasma inconspicua. The stromatoporoids includeEcclimadictyon nestori Pseudostylodictyon inequale and Stromatocerium sp. Silicified trilobitesinclude Pliomerina austrina Remopleurides saenuros, Pseudobasilicus sp., Amphilichas sp.,Sphaerocoryphe sp., Parkesolithus sp., ?Encrinuraspis and fragmentary asaphids.

distance 19 km, time interval 25 min.

Barbeque lunch at historic Nelungaloo Station, kindly provided by Mr and Mrs J.M. Barnes.

STOP 5 TSR quarry - Cotton Formation. Bolindian graptolites. (L. Sherwin)

30 minutes.

Ref.- Sherwin 1973, Krynen et al., 1990.

The fine grained siliceous sediments in this gravel scrape are more typical of sediments in the nonvolcanic Ordovician sequences. Nearer Forbes and north-west of Parkes sediments of this typeoverlie or are in contact with shoshonitic volcanics. The following graptolites have beenidentified: - Dicellograptus cf. elegans, Climacograptus supemus, Cl. hastatus Climacograptus sp.,Orthograptus sp. Riva (pers. comm.) has queried this occurrence of C. supernus in a Pacific faunalprovince.

STOP 6 Burrawang Road - Cotton Formation. Bolindian graptolites and brachiopods. (L.Sherwin, I. Percival)

20 minutes.

Ref.- Sherwin 1973, Percival 1978.

The sediments at this locality are much as last, being slightly younger. The only graptolite found

47

at this locality is Climacograptus normalis and it is just possible that this locality is earliestSilurian in age. This is also the type locality for the inarticulate brachiopod Paterula giganta.

STOP 7 Cottons Hill - Cotton Formation. Llandovery graptolites, trilobites and brachiopods.

30 minutes

Ref.- Sherwin 1973, 1974.

The sediments here are much as at the last two localities, being if anything slightly less cherty.The graptolites indicate a late Llandovery age (turriculatus zone), the earliest part of the Silurianbeing obscured by the alluvium between this and the preceding locality. Early Llandovery(cyphus zone) graptolites are known from the Cotton Formation north-west of Parkes (Sherwin1976). Opinion is divided as to whether the Cotton Formation is continuous across theOrdovician - Silurian boundary (Sherwin 1973, Krynen et al., 1990) or not (Webby 1976).

The low rise about 500 metres to the north-west is a coarse conglomerate at the base of the ForbesGroup of Wenlock age. The low rise about three kilometres due west is the Calarie Sandstonemarking the base of the Late Silurian - Early Devonian Derriwong Group. The ridge on thewestern horizon is Late Devonian sandstone.

Return to Parkes via Forbes or Ben Hall place and Gunningbland.

Overnight at the Court Street Motel

DAY 6 Sunday 14 July

STOP 1 - Visit to Geopeko Mine Office

Geopeko have been carrying out intensive exploration in the Parkes district for many years, overwhich time they have proven up several major ore deposits, all related to the Ordovicianmagmatism of the Parkes Platform. They have not yet commenced development of any of theirproposed mines, but expect to commence commercial production within the next year. Copper andgold are the two main resources, with over $1 billion contained metal in the ground for eachelement. Geopeko geologists will explain their operation and show us some of their drill core.

At about 11.00AM we set off for Sydney, stopping in the Blue Mountains for lunch and to viewsome of the spectacular scenery where the Permian Sydney Basin sandstones have been uplifted toover 1000m and cut by deep gorges.

48

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