Late Middle Cambrian trilobites from St Valentines Peak and Native Track Tier, northwestern Tasmania
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JAMES B. JAGO, JIN-SONG B A O A N D PETER W. BAILLIE JAC,O, J. B., BAO,J.-S. & BAILLIE,P. W., 30.4.2004. Late Middle Cambrian trilobites from St Valentines Peak and Native Track Tier, northwestern Tasmania. Alcheringa 28, 2152. ISSN 0311-5518 Late Middle Cambrian trilobites are described from two localities in northwestern Tasmania. Twenty-four trilobite taxa are documented. The 15 agnostoid species include Paraclavagnostus longus sp. nov. which is placed in the Utagnostinae, a new subfamily of the Clavagnostidae. The nine polymeroid species include a new member of the Rhyssometopidae, Tasmana truncata gen, et sp. nov. Three other new species of polymeroids are erected: Fuchouia tasmaniensis, Nepea delicata and Nepea hellyeri. Both faunas correlate with the Lejopyge laevigata Zone on the northern Australia biostratigraphie scale, possibly with the L. laevigata II Zone. When compared with Hunan, China, correlation is with the upper part of the Lejopyge laevigata Zone, and particularly with the lower part of the Proagnostus bulbus Zone.
James B. Jago O'
[email protected]), Jin-Song Bao, School of Natural and Built Environments, University of South Australia, Mawson Lakes, South Australia 5095; Peter g(. Baillie (
[email protected]), TGS-NOPEC, Level 5, 1100 Hay Street,WestPerth, WesternAustralia 6005 (previous address Mineral Resources Tasmania, Rosny Park, Tasmania); received 20.3.2003, revised 6.6.2003. Key words: Late Middle Cambrian, Tasmania, correlation, trilobites, new taxa LATE MIDDLE CAMBRIAN trilobites from near St Valentines Peak and from Native Track Tier in northwestern Tasmania, Australia (Fig. 1) are described. Although a substantial number o f late Middle Cambrian agnostoid trilobites have been described from Tasmania (Jago & Daily 1974; Jago 1976a, 1976b, 1977; Jago & Brown 2001) only a few polymeroid trilobites have been described in any detail ( Jago 1972, Jago 1974, Jago & Brown 2001). Both localities occur on the St Valentines 1:50 000 map sheet (Seymour 1989). The Cambrian rocks near St. Valentines Peak are exposed in the core o f an anticline (Jago et al. 1975, Baillie et al. 1986), and comprise siltstone, chert, sandstone, rhyolitic welded tuff and an impure limestone metamorphosed by Devonian granite. A siliceous siltstone, which is probably near the base o f the exposed succession, is richly fossiliferous at ffrid 0311/5518/2004/01021-32 $3.00 © AAP
reference CQ945205 on the St Valentines Peak 1:50 000 geological map (Baillie et al. 1986). The St Valentines Peak fauna contains the following trilobites: Ammagnostus laiwuensis (Lorenz, 1906), Proagnostus bulbus Butts, 1926, Lisogoragnostus sp., Clavagnostus calensis R u s c o n i , 1950, A s p i d a g n o s t u s sp. 1, Paraclavagnostus longus sp. nov., Oidalagnostus changi Lu, 1964, Valenagnostus imitans (Opik, 1961), Helepagetia argusi (Jago, 1972), Schmalenseeia gostinensis Jago, 1972, Fuchouia tasmaniensis sp. nov., Bathyuriscus sp., Nepea hellyeri sp. nov., Penarosa sp., Tasmana trunacata gen. et sp. nov., Ceratopygidae gen. et sp. indet, and Leichneyella? sp. Schmalenseeia gostinensis Jago, 1972, Helepagetia argusi (Jago, 1972) and most o f the agnostoid trilobites were described by Jago ( 1972, 1976a) and Jago & Daily (1974). Extra information is given here on the a g n o s t o i d trilobites and the r e m a i n i n g
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Helepagetia argusi (Jago, 1972), Fuchouia tasmaniensis sp. nov. and Nepea delicata sp. nov.
Age of Faunas
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Fig. 1. Locality map, Tasmania, Australia.
polymeroids are described. The Native Track Tier locality is at grid reference DQ140218 as shown on the St. Valentines 1:50 000 geological map (Baillie et al. 1986). The Middle Cambrian geology of the area was described by Seymour (1989). In referring to the Middle Cambrian rocks Baillie (in Seymour 1989, p. 19) noted that "two broad associations can be recognised in the Native Track Tier area". The first of these is dominantlyvolcanic and the second is a mixed volcano-sedimentary succession. Baillie & Jago (in Seymour 1989,p. 147) noted that the fossils come from within a mixed succession of felsic volcanics and sedimentary rocks. The well-preserved fossils are found as internal and external moulds within a buffor fawncoloured siltstone which occurs within a conglomerate-sandstone-siltstone succession. Baillie & Jago (in Seymour 1989, p. 147) stated that the poor outcrop does not allow a meaningful facies analysis of the succession. The Native Track Tier fauna contains the following trilobites: Innitagnostus sp., Ammagnostus laiwuensis (Lorenz, 1906), Proagnostus bulbus Butts, 1926, Clavagnostus burnsi Jago & Daily, 1974, Aspidagnostus sp. 2, Glaberagnostus sp., Valenagnostus imitans (0pik, t96t), Oidalagnostus cf. changi Lu, 1964, agnostoid gen. et sp. indet. 1, agnostoid gen. et sp. indet. 2, agnostoid gen. et sp. indet. 3,
The two faunas described herein have several key agnostoid species in common and are thus of very similar age. In South China (Hunan Province), Peng & Robison (2000) showed that Ammagnostus laiwuensis ranges from the upper Ptychagnostus atavus Zone to the middle of the Proagnostus bulbus Zone (about equivalent to the base of the Acmarhachis quasivespa Zone in northern Australia; see Fig. 2). At Christmas Hills, in northwestern Tasmania, A. laiwuensis occurs in faunas ofLejopyge laevigata I and II age (Jago 1976a). The species is known from China, Australia, Canada, Greenland and possibly Antarctica (Peng & Robison 2000). Proagnostus bulbus is a widespread species occurring in Australia, Canada, China, Greenland, Kazakhstan, Russia and the USA. Proagnostus bulbus ranges from the Proagnostus bulbus Zone to about the middle of the Linguagnostus reconditus Zone of Hunan, South China (Peng & Robison 2000), or in the Australian context from the Lejopyge laevigata Zone to the Acmarhachis quasivespa Zone. Paraclavagnostus was originally described from the late Middle Cambrian Lejopyge laevigata Paraclavagnostus variatus Zone of Sichuan Province, China (Yang et al. 1991). As noted below, all known species of Paraclavagnostus are of latest Middle Cambrian age, equivalent to Lejopyge laevigata Zone on the northern Australian biostratigraphic scheme. Paraclavagnostus is similar to Utagnostus Robison, the type species of which was first described from the upper part of the late Middle Cambrian Bolaspidella Zone of Utah (Robison 1964). Lisogoragnostus is a very widespread genus ranging from the Ptychagnostus atavus Zone to the late Idamean Stigmatoa diloma Zone on the northern Australian biostratigraphic scheme (Peng & Robison 2000). Clavagnostus calensis is a distinctive, but uncommon species, known from Argentina,
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Tasmania, Antarctica and China. It is everywhere of a similar late Middle Cambrian Lejopyge laevigata Zone age. Clavagnostus burnsi w a s first described from Riana, in northwestern Tasmania, by Jago & Daily (1974) who suggested
a Glyptagnostus stolidotus Zone age. However, Bao (1995) suggested that the Riana fauna is in the range ofLejopyge laevigata III Zone to lower Acmarhachis quasivespa Zone. Oidalagnostus changi is known from Hunan.
SOUTH CHINA
)RTHERN AUSTRALIA I
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