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Records of the Western Australian Muselll1l Supplement No. 58: 59-63 (2000).

A new Early Ordovician trilobite from the Broken River region,northeastern Australia: taxonomy and palaeogeographic implications

Raimund Feist1 and John A. Talenf1 Institut des Sciences de l'Evolution, UMR 5554 du CNRS, Universite de Montpellier II,

34095 Montpellier Cedex 05, France2 Macquarie University Centre for Ecostratigraphy and Palaeobiology (MUCEP),

Department of Earth and Planetary Sciences, Macquarie University 2109, Australia

Abstract - A trilobite from an olistolithic slab of Ordovician shallow waterlimestone in the Big Stockyard Creek area south of Greenvale in the BrokenRiver Province, northeastern Australia, is a new representative of thesubfamily Asaphinae: Norasaplllls (Shergoldina) greenvalensis subgen. nov. andsp. nov. Due to close morphological relation to previously describedNorasaphus from the Nora Formation of central Australia, a late EarlyOrdovician age is inferred for the trilobite-bearing horizon-the first recordof Early Ordovician shelly faunas from northeastern Australia. The age­spectrum of Ordovician-Silurian carbonate olistoliths and clasts in debrisflows of the Broken River region is increased by the recognition of a lateEarly Ordovician age for the host olistolith. The "lost" Georgetown Blockcarbonate platform is now inferred from this occurrence to have been inexistence through much or all of the time-interval from late Early Ordovicianuntil at least earliest Wenlock times. Autochthonous and allochthonouscarbonate units in the southwestern Broken River Province (west of the GreyCreek Fault Zone) confirm that a carbonate platform (or platforms) persisted,intermittently, in the Broken River Province/Georgetown Province until atleast two-thirds of the way through Devonian times, until around theGivetian-Frasnian boundary.

GEOLOGIC AND PALAEOGEOGRAPHICSETIING (JAT)

The limestone body (Figure 1), source of thetrilobite described herein, is one of severallimestone occurrences, all regarded by us asallochthonous, within a sequence of volcaniclasticarenites and breccias, siltstones, mudstones andcherts with, locally, quartzose arenites, referred toas the Carriers Well Formation by Withnall et aL(1988, 1992, 1993). Most areas shown as substantiallimestone bodies on previous mapping have provedto consist of limestone cobbles and blocks in amatrix of clastics, as in the tract of "Carriers WellFormation" west of and running parallel to GreyCreek between Dinner Creek and Greenvale, andextending southwards across Little Stockyard andBig Stockyard Creeks for about 12 km. Adjacenttracts of mudstone, quartzose arenite and minoraltered basalt and jasper, seemingly withoutlimestone olistoliths, have been referred to asWairuna Formation (Withnall et al. 1988, 1992,1993).

Ordovician limestones occur also asallochthonous slabs in the Crooked CreekConglomerate (Withnall et al. 1992, 1993) about 17km west of the olistolithic slab from which thetrilobite described here was obtained, and as

cobbles and small olistoliths in the Perry CreekFormation, notably in Thatch Creek (Sloan et al.1995) about 45 km east of the Big Stockyard Creeklimestone olistoliths. These occurrences we view ashaving been derived from a now-lost carbonateplatform, formerly located on the Georgetown Blockwest of the Grey Creek Fault Zone and HallsReward Fault (the northwest boundary of theBroken River Province).

The trilobite, a single cranidium, is the first reportof Early Ordovician trilobites from northeasternAustralia. Though representing a new taxon, itsrelationships with asaphines described by Forteyand Shergold (1984) from the lower Nora Formation(Toko Syncline, Central Australia) indicate a lateEarly Ordovician age for the horizon.

This occurrence dates the particular olistolithicslab as being substantially older than the age­spectrum presently assumed for limestones in theGrey Creek-Dinner Creek-Greenvale tract of"Carriers Well Formation" from which LateOrdovician Caradoc-Ashgill-?earliest Llandoveryconodonts have been reported (Withnall et al. 1993;Andrew Simpson, pers. comm). It is also olderthan the Ashgill-Iatest Llandovery\earliestWenlock age of clasts and olistoliths in the PerryCreek Formation (Sloan et al. 1995) of the

60 R. Feist, J.A. Talent

1900'

Fault

Proterozoic

Ordovician-Early Silurian and ?Cambrian

t00I

4I

2I

kilometres

Road, track

Volcanics connected with 'Carriers Well' andWairuna Formations, principally Everetts CreekVolcanics

Limestone olistoliths and areas with salientdebris flows with limestone boulders ('CarriersWell' Formation) (late Earty Ordovician to earliestSilurian)

Arenites and cleaved mudstones of the 'CarriersWell', Wairuna and Judea Formations (notdifferentiated)

oI

Metamorphics, including the igneous GrayCreek Complex

Detail: Sections UBB and UBC

Location

oo

Early Carboniferous (Tournaisian)

~..'. . Teddy Mountain or Venetia Formation arenitesL--.J with subordinate conglomerates, slltstones,

shales and rare carbonates

Quaternaryo Alluvials

Figure 1 Distribution of Ordovician limestones in relation to stratigraphy in the Gray Creek-Big Stockyard Creek areasouth of Greenvale, northeastern Queensland (modified from Withnall et al. 1992).

Christmas Creek-Thatch Creek area 45 km to theeast, and the Llandovery-earliest Wenlocklimestone clasts in the Quinton Fomation 15 km tothe south-southwest (Simpson 1999). All these

allochthonous limestones are inferred to have beenderived from the "lost" Georgetown CarbonatePlatform to the west. The age-spectrum ofOrdovician-Silurian carbonate olistoliths and clasts

F-------~

Early Ordovician trilobite, NE Australia

in debris flows of the Broken River region is thusincreased by the recognition of a late EarlyOrdovician age for the host olistolith. The "lost"Georgetown Block carbonate platform is nowinferred from such data to have been in existencethrough much or all of the time-interval from lateEarly Ordovician until at least earliest Wenlocktimes and, from the record of autochthonous andallochthonous carbonate units in the southwesternBroken River region, to have continued to existuntil at least two-thirds of the way throughDevonian time%until around the Givetian­Frasnian boundary (Mawson and Talent 1989,1997; Sloan et al. 1995; Feist and Talent, 2000).

SYSTEMATIC DESCRIPTION (R.F.)

Family ASAPHIDAE Burmeister 1843

Subfamily Asaphinae Burmeister 1843

Genus Norasaphus Fortey and Shergold 1984

Type speciesN. (N.) skalis Fortey and Shergold 1984

Subgenus Shergoldina subgen.nov.

Type speciesN. (Sltergoldina) greenvalensis sp. novo

DiagnosisA subgenus of Norasapltus with quadrangular,

axially keeled glabellar frontal lobe and withstriated surface sculpture.

Derivation of nameAfter John H. Shergold who made major

contributions to the knowledge of Australian EarlyPalaeozoic trilobites

DiscussionThe new taxon is an asphid related to Basiliella

Kobayashi 1934 and allies, especially as regards theoverall shape of the forwardly expanding glabella,disposition of the groove-like IP apodemal furrows,and the clearly demarcated occipital ring. It ischaracterised by the surface sculpture of itsexoskeleton. Indeed it is so far the only knownasaphid displaying terrace lines parallel to the axison the entire cranidial prosopon. The originalconcept of the sculpturless nature of as aphids, asdiagnosed by Jaanusson (in Moore 1959: 334) waschallenged by Fortey and Shergold (1984:328) whenthey described Norasaphus and Norasaphites fromCentral Australia, both with tuberculate prosopons.The orientation of terrace ridges parallel to thesagittal line in the new taxon is exceptional as these

61

ridges are generally arranged transversely (forexample, in Ningkianites Lu 1975: 317)

A further peculiarity of Shergoldilla is the presenceof a keeled glabella. This is unusual in asaphinesbut, due to incomplete knowledge of the taxon, it isnot clear if this feature is specific or supraspecific.Most other cranidial traits indicate closerelationship to Norasaphus, so it is regarded as asubgenus of the latter. This attribution should bereconsidered when information becomes availableregarding the librigena and pygidium.

Features such as the forwardly expandingglabella with modified glabella furrows thatcharacterise Norasaphus have been considered tobe a morphological adaptation (of phacomorphtype) often found in trilobites adapted to inshorecarbonate fades of epeiric seas (Fortey and Shergold1984, Fortey and Owens 1990). Occurrence of thenew phacomorph taxon in shallow waterOrdovician limestones in the Broken River region istaken to be another example of this phenomenon.

Norasaphus (Shergoldina) greenvalensis sp.nov.Figures 2A-D, 3

DiagnosisAs for the subgenus.

Derivation of nameFrom discovery south of Greenvale, northeastern

Australia.

HolotypeCranidium, Australian Museum, Sydney, AMF

107560, Figures 2A-D, 3.

MaterialA single undeformed cranidium of adult size

displaying the external cuticular surface, preservedin limestone, deposited in the Australian Museum,Sydney (AMF 0000).

Locality and ageBig Stockyard Creek, south of Greenvale,

northeastern Queensland, Australia (Figure 1);Early Ordovician.

DescriptionCranidium elongate rectangular, anteriorly as

wide as the width across the palpebral lobes, withprotruding posterior fixigenae. Anterior glabellalobe quadrangular, with broadly curved, slightlytruncate outline anteriorly, sharply delimitedlaterally by deep dorsal furrows parallel to thesagittal line, and to the rear by the anteriorterminations of large, rather deep axial furrows (IP)that converge slightly backwards on both sides of

62 R. Feist, J.A. Talent

A

Figure 2 Norasaphus (ShergoldinaJ greenvalensis sp.nov.Holotype, Australian Museum, Sydney, AMF107560. A, dorsal view, external mould, x 3.2;B, lateral view, x 4.7; C, frontal view, x 4.2

the transversely arched, narrow, elongate basalglabella lobe. Inflated ovoid, lateral lobes ofinnerglabellar origin are separated from central partof basal glabella lobe by continuous, curved groovesthat merge with the posterior ends of the 1Pfurrows and meet the occipital furrow. In lateralview, the frontal lobe of the glabella is elevated,highest at its posterior end, steeply down bentanteriorly. Posterior part of glabella continuouslydeclining to the rear, merging centrally with theoccipital lobe. Crestline of glabella defined by anarrow keel that runs from the front to the rear,vanishing behind; glabella in frontal view roof likecentrally, down curved abaxially. Genal lobesinflated, elongate, converging anteriorly andextending to the anterior end of the palpebral lobes,separa ted from basal glabella by shallow,·outwardly curved dorsal furrows running into 1Pgrooves anteriorly and meeting the lateral ends ofthe occipital furrow. Occipital furrow very shallowmedially, deepening behind lateral lobes of glabellabase. Occipital ring cylindrical, of uniform width,slightly inflated abaxially. Palpebral lobes small,elevated above highest level of frontal glabella lobe,steeply inclined adaxially, close to dorsal furrows.Preoccular sutures, parallel to each other, meet theanterior border at an obtuse angle. Anteriorfixigenae narrow, of equal width from rear to front,slightly vaulted traversely, gently decliningforwards then strongly bent downwards in front tothe narrow, slightly concave anterior border. Borderin front of glabella slightly declining forward withanterior edges that meet at mid-line with a largeobtuse angle. Border furrow continuously deep;preglabellar field absent. Entire surface sculpturedwith dense, slightly anastomosing, long terraceridges of equal strength, all orientated parallel tothe sagittal line.

B

c

ComparisonThe new species resembles the type species of

Norasaphus, N. (Norasaphus) skalis Fortey andShergold 1984 in the general outline of theforwardly expanding glabella and the deep 1Papodemal furrows. However, there are major traitsdistinguishing the new taxon, such as thequadrangular, keeled anterior glabella, the swollenbasal glabella lobes, and the narrow, parallel-sidedanterior fixigenae. Unlike all species of Norasaphusfrom central Australia, no tubercular sculpture isdeveloped. It is anticipated that the new taxon willeventually be accorded full generic status; however,this should be considered only when the pygidiumis known.

Figure 3 Norasaphus (ShergoldinaJ greenvalensis sp.nov.Reconstruction of the cranidium. Bar scale: 1mm.

ACKNOWLEDGEMENTS

RF is grateful to Macquarie University for aresearch grant enabling him to undertake field work

Early Ordovician trilobite, NE Australia

with JAT, Ruth Mawson, Andrew Simpson, BrettPyemont, Ken Bell and Ross Drury and otherMUCEP colleagues, focused on a quest for faunasin the Ordovician limestones of the Broken Riverregion of northeastern Australia. Thepalaeontological interpretations profited fromfruitful discussions with John H. Shergold. Thedrawing was made by L. Meslin (Montpellier);Michel Pons (Montpellier) printed the photographsof the trilobite. This is a contribution to ISEM, UMR5554 CNRS and to two International GeologicalCorrelation Program projects: IGCP 410 The greatOrdovician biodiversification event and IGCP 421North Gondwana mid-Palaeo20ic bioevent \ biogeographypatterns in relation to crustal dynamics

REFERENCES

Feist, R and Talent, J.A. (2000). Devonian trilobites fromthe Broken River region of northeastern Australia.Records of the Westem Australian Museum SupplementNo. 58: 65-80.

Fortey, R. A. and Owens, R. M. (1990). Evolutionaryradiations in the Trilobita. In P.D. Taylor and G.P.Larwood (eds), Major Evolutionary Radiations.Systematics Association Special Volume 42: 139-164.

Fortey, RA. and Shergold, J. H. (1984). Early Ordoviciantrilobites, Nora Formation, central Australia.Palaeontology 27: 315-366.

Kobayashi, T. (1934). The Cambro-Ordovician formationsand faunas of South Chosen. Palaeontology, Part B.Lower Ordovician faunas. Joumal of the Faculty ofSciences, University of Tokyo 2 (3): 521-585.

Lu Yen-Hao (1975). Ordovician trilobite faunas of centraland southwestern China. Palaeontologia Sinica 152 B(11): 1--463.

Mawson, R. and Talent, J.A. (1989). Late Emsian-Givetianconodont stratigraphy and biofacies~arbonateslopeand offshore shoal to lagoon and nearshore carbonateramp-Broken River, north Queensland, Australia.Courier Forschungsinstut Senckenberg 117: 205-259.

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Mawson, R. and Talent, J.A. (1997). Famennian­Tournaisian conodonts and Devonian-EarlyCarboniferous transgressions and regressions innortheastern Australia. Geological Society of AmericaSpecial Paper 321: 189-233.

Simpson, A. (1999). Early Silurian conodonts from theQuinton Formation of the Broken River region (north­eastern Australia). Abhandlungen der GeologischemBundesanstalt 54: 181-199.

Sloan, T.R., Talent, J.A., Mawson, R., Simpson, A.J.,Brock, G.A., Engelbretsen, M.J., Jell, J.5., Aung, A.K.,Pfaffenitter, C, Trotter, J. and Withnall, l.W. (1995).Conodont data from Silurian-Middle Devoniancarbonate fans, debris flows, allochthonous blocksand adjacent autochthonous platform margins:Broken River and Camel Creek areas, northQueensland, Australia. Courier ForscJl1lngsinstitutSenckenberg 182: 1-77.

Withnall, l.W. (1993). Camel Creek Special 1:250,000geological map. Queensland Department of Mineralsand Energy, Brisbane.

Withnall, l.W., Lang, S.C, Draper, n, Fielding, CR., Jell,J.S., Talent, J.A., Mawson, R., Fleming, P.J.G.,Simpson, A., Blake, P.R., Humphries, M., Jorgenson,P., Grimes, K.G., and Scott, M. (1993). Geology of theBroken River Province, north Queensland. QueenslandGeology 4: 1-289.

Withnall, l.W., Lang, S.C, Jell, J.5., McLennan, T.P.T.,Talent, J.A., Mawson, R, Fleming, P.J.G., Law, S.R,Macansh, J.D., Savory, P., Kay, J.R and Draper, J.J.(1988). Stratigraphy, sedimentology, bio­stratigraphy and tectonics of the Ordovician toCarboniferous Broken River Province, northQueensland. Australasian Sedimentologists GroupField Guide 5: 1-200.

Withnall, l.W., Lang, S.C and 12 others (1992). BrokenRiver Special 1:100,000 geological map. Brisbane,Queensland Department of Resource Industries.

Manuscript received December 1999; accepted MarcJz 2000.