The Early Ordovician trilobite genus jujuyaspis in Australia  

SHERGOLD,J.  

Jujúyaspis, a stratigraphically useful trilobite for the definition of the earliest Ordovician, has been identified in the onshore Bonaparte Basin of northeastern Western Australia. It occurs in single collections (JSK251 and JSK268) from two sections (CG231 and CG249) in the Pander Greensand at Clark Jump Up, on Carlton Hill Station, 39 km north of Kununurra. The Pander Greensand, the youngest outcropping CambrianOrdovician formation of the Bonaparte Basin, is a deeply weathered, highly glauconitic quartz sandstone, approximately 125 m thick at section CG249.

Jujuyaspis is a component of Faunal Unit XII in the informal biostratigraphic scheme proposed for the Ord and Bonaparte Basins by Opik (in Kaulback and Veevers, 1969). This Unit contains three distinct faunal assemblages. The earliest one, possibly of terminal Cambrian, latest Datsonian or earliest Warendan age, in Australian stadial nomenclature, contains Aristokainella cf A. calvicepitis Zhou and Zhang, 1978, and undetermined species of Hystricurus (Hystricurus), Leiostegium (L.eiostegium) and Yosimuraspis. The second assemblage consists of Aristokainella cf A. calvicepitis, and undetermined species of JiJia? Jujúyaspis, Leiostegium (Leiostegium) and Parpilekia? This has an early Ordovician, early Warendan age, within the Cordylodus lindstromi conodont zone. The youngest trilobite assemblage of Unit XII, comprising Tienshihfuia cf T. constricia Kuo and Duan, 1982, and undetermined species of Apatokephalops and Asaphellus, is associated with conodonts which include Cordylodus angulatus, Chosonodina berfurthi, Drepanoistodus and Rossodus? which confirm a late Warendan age within the Cordylodus angulatus-Chosonodina berfurthi Zone.

The two collections which have yielded Jujuyaspis contain six cranidia, two librigenae and thirteen pygidia. Cranidia are all incomplete and details of the preglabellar morphology cannot be documented with confidence. Neverthless, the tagma is transversely moderately convex. The glabella is anteriorly gently tapered and bluntly rounded, extending to the anterior cranidial margin; the glabellar furrows are effaced and the occipital furrow only faintly indicated. The occipital ring is relatively narrow (sag.), is not raised above the dorsal of the glabella in profile, and lacks a median node. Palpebral lobes are short (exsag.), and situated close to the glabella, anterior to the midlength of the glabella. The posterolateral limbs are expansive and bluntly rounded, and bear posterior border furrows which widen slightly distally. The preocular fixigenae are much restricted, and may not connect anteriorly. The librigenae are characterised by small eyes, and have prominent lateral border furrows. There is no genal spine or even a prominent genal angle. Pygidia are parabolic or slightly subtriangular, have low convexity (tr.) and entire, nonspinose, margins. There are three axial rings and an ill-defined terminal piece, not extending to the posterior margin. Pleural and--interpleural furrows are effaced and there is no border furrow

The type species of Jujuyaspis, J. keideli Kobayashi, 1936, and its synonyms (according to Aceñolaza and Aceñolaza, 1992), occurs in Argentina, Bolivia, Colombia and Norway where Nikolaisen and Henningsmoen (1985) recognised J. keideli norvegica, J. angusta Henningsmoen, 1957 also occurs in Norway. In North America, J bocealis Kobayashi, 1955 occurs in British Colombia, Alberta, Utah and Texas. J. colombiana

Baldis et al., 1984 occurs in Colombia, and J. sinensis Zhou, 1980 (in Chen et al., 1980) occurs in Hebei, China. Nikolaisen and Henningsmoen (1985) also consider Alimbataspis kelleri Balashova, 1961 from Aktyubinsk, Kazakhstan, to be a species of Jujuyaspis. Furthermore, the fragments described by Shergold and Sdzuy (1991) as olenid genus and species undeterrnined, from Celtiberia, Spain, also seem likely to represent this genus. Everywhere, species of Jujuyaspis occur close to the beginning of the Tremadoc, being either associated with subspecies of Rhabdinoporaflabelliforme or conodonts of the Cordylodus lindstromi Zone.  

References  

Ace   Aceñolaza, F G. and Aceñolaza, G. F,1992. The genus Jujuyaspis as a world reference fossils for the Cambrian-Ordovician boundary. In: Webby, B. D. and Laurie, J. R. (Eds) Global Perrpectives on Ordovician Geotogy, 115 -120. Balkema, Rotterdam.

Balashova, E. A.,1961. Some Tremadocian txilobites from the Aktyubinsk region. AkademiyaNauk SSSR, Trudy Geologicheskogo Instituta, 18, 102-145 [In Russian].

Baldis, B., Gonzalez, S. and Perez, V, 1984. Trilobites tremadocianos de la Formacion Negritos (Perforacion La Heliera), Llanos de Colombia. 3rd Latinamerican Congress, Paleontotogy, Mexico, Memoirs 28-41.

Chen Jun-yuan and nine others,1980. Outline of the Ordovician deposits and faunas of Shandong, N. Anhui and N. Jiangsu, E. China. Academia Sinica, Nanjing Institute of Geotogy and Palaeontology, Memoir 16, 15 9-195.  

Henningsmoen, G., 1957. The trilobite Family Olenidae. Skrifter utgitt av det Norske Videnskaps­Akademi i Oslo. 1 Matematisk-naturvidenskapelig klasse, 1957, 1, 303 pp.

Kaulback, J. A. and Veevers, J. J.,1969. Cambrian and Ordovician geology of the southern part of the Bonaparte Gulf Basin, Western Australia. Bureau of Mineral Resources of Australia, Report 109, 80 pp.

Kobayashi, T, 1936. On the Parabolinella fauna from Province Jujuy. Argentina, with notes on the Olenidae. japanese, journal of Geology and Geography, 13, 85-102.

Kobayashi, T.,1955. The Ordovician fossi1s from the McKay Group in British Columbia, western Canada, with a note on the Early Ordovician palaeogeography. journal of the Faculty of Science, University of Tokyo, 11, 9 (3), 493 pp.

Kuo Hung-chun, Duan Ji-yi and An Su-lan, 1982. Cambrian-Ordovician boundary in the North China Platform with descriptions of trilobites. Paper for 4th International Symposium on the Ordovician System, Dept Geology, Changchun University, China, 31 pp.

Nikolaisen, F and Henningsmoen, G,1985. Upper Cambrian and lower Tremadoc olenid trilobites from Digermul Peninsula, Finmark, northem Norway. Norges geologiske undesokelse, Bulletin 400, 49 pp.

Shergold, J. H. and Sdzuy, K.,1991. Late Cambrian trilobites from the Iberian Mountains, Zaragoza Province, Spain. Beringeria, 4,193-234.

Zhou Zhiyi and Zhang Jinlin, 1978. The Cambrian-Ordovician boundary of the Tangshan area with descriptions of the related trilobite fauna. Acta Palaeontologica Sinica, 17, 10-23 [In Chinese], 23-26 [In English].