Chitinozoans and Associated Conodonts from the Early Devonian Point Hibbs Formation, Tasmania, Australia

Records of the Western Australian Museum Supplement No. 58: 163-177 (2000). Chitinozoans and associated conodonts from the Early Devonian Point Hibbs Formation, Tasmania, Australia. 1 Theresa Winchester-Seeto and Stephen P. Carey2 I Centre for Ecostratigraphy and Palaeobiology, Department of Earth and Planetary Sciences, Macquarie University, 2109. Australia. [email protected] 2 Geology Department, University of Ballarat, P.o. Box 663, Ballarat, Vie. 3353, Australia. e-mail: [email protected] Abstract - Chitinozoans from the Early Devonian Point Hibbs Formation are described and illustrated; associated conodonts are illustrated for the first time and conodont evidence for dating is reviewed. The chitinozoan species Bulbochitina bulbosa Paris, which has been used as an index species for the late Pragian by Paris et al. (1999) in their global biozonation of the Devonian, occurs in the middle part of the Point Hibbs Formation. Previous studies have shown that the oldest B. bulbosa occurs low in the kindlei Conodont Zone, and the presence of this species suggests that the middle and upper part of the Point Hibbs Formation belong to the kindlei Conodont Zone or higher. Chitinozoan species recovered from Tasmania include those with representatives in western France, Bohemia, Poland, Victoria and northern Queensland. INTRODUCTION Burrett 1984; Carey and Berry 1988), Point Hibbs is a promontory on the isolated west microvertebrates (Burrow et al. 1998), linings of coast of Tasmania. The rocks at Point Hibbs and agglutinated foraminifera (Bell and Winchester along the adjacent coast range in age from Seeto 1999 in press), chitinozoans (described herein) Precambrian to Jurassic, and are juxtaposed along and scolecodonts. southeasterly-dipping thrust planes (Brown et al. Although the lower part of the Point Hibbs 1991; Carey and Berry 1988; McClenaghan et al. Formation has been interpreted as belonging to the 1994). Of the three Devonian units present, only the sulcatus Conodont Zone by many workers, the age Point Hibbs Formation is predominantly limestone. of the upper part was uncertain. The impetus of this The Point Hibbs Formation occurs in two separate study was to document the chitinozoans and to use fault slivers at Sanctuary Bay and at 'Clearwater them to further refine the dating of the Point Hibbs Point' (Figure 1). Formation. The Point Hibbs Formation consists of fossiliferous lime packstone interbedded with calcareous terrigenous mudstone in nearly equal METHODS proportions (Carey 1989; Carey and Berry 1988). Details of the sections used in this study are Both rock types are thinly bedded and richly provided in Carey and Berry (1988), with the fossiliferous, and locally the packstone is partially 'Clearwater Point' section in the north, and a replaced by dolomite. composite of three sections correlated by marker Early Devonian macrofossils from this area have horizons comprising the Sanctuary Bay section. The been the subject of several studies, especially the samples were collected by Steve Carey in 1985 for corals which dominate much of the outcrop (Hill sedimentological studies and for further conodont 1942; Jell and Hill 1970; Pedder 1998; Pedder and work; the same samples were subsequently McLean 1982), and brachiopods (Flood 1974). The investigated for chitinozoans. fauna also comprises bryozoans, echinoderms, Methods of processing for chitinozoans follow tentaculitids, gastropods, bivalves, ostracodes and those outlined by Paris (1981), including initial trilobites. The environment of deposition is treatment of 50 g of crushed rock with lO°/" HCl interpreted as being open marine, below normal until all the carbonate has been dissolved, followed wave base, as evidenced by the abundance of mud, by acid digestion by 70'10 HF for 12-48 hours. which was disturbed episodically by storm Concentrated nitric acid was used when necessary turbulence (Carey and Berry 1988). The microfauna for surface etching, dissolution of fluoride salts and comprises conodonts (Philip and Pedder 1968; the destruction of amorphous organic matter. The 164 T. Winchester-Seeto, S.P. Carey HIBBS BAY JURASSIC CLEARWATER BAY W Dolente CARB.. PERMIAN 'CLEARWATER POINT ~ Lower Parmeener Supergroup LOWER DEVONIAN ~ POint Hlbbs Formalion PYRAMID M.• U. ORDOVICIAN ISLAND ~ ~ Gordon Group U CAMBRIAN . L ORDOVICIAN ~ ?Denlson Gp Owen Conglomerate CAMBRIAN 1------=="'------..... ~~i~~~ Arglllite 110 Bedding attitude f 1Of Fault plane atlitude Fault Fault Inferred 41·S o 500 m POINT - - -- HIBBS 43'S Figure 1 Locality map, Point Hibbs, Tasmian showing geology along the coastline and position of 'Clearwater Point' and Sanctuary Bay section (from Carey and Berry 1988). residue was then separated through a 53pm sieve specimens are, in general, moderately well and picked with a micropipette. Representatives of preserved, though some of the thinner-walled each species were selected and mounted onto a stub specimens show compression and some have with carbon tape for photography using an considerable erosion of ornament; specimens of Environmental Scanning Electron Microscope (E Bulbochitina bulbosa Paris are more robust, and SEM) Model E-3. consequently withstood compaction and diagenesis better (figures 5, 6). The chitinozoans were extracted from the fossiliferous lime packstone, with large RESULTS bioclasts of brachiopods and other macrofauna. Nine species of chitinozoans were extracted from They were preserved in fine mud matrix between three samples of the Point Hibbs Formation (figures the bioclasts, possibly resulting from a fine "rain" 2-4); two samples of the Point Hibbs Formation and of mud and organic matter drifting down after the one sample from the Gordon Group were barren. bioclasts had been deposited. The organic-walled Well preserved scolecodonts and linings of microfossils were all dark-brown to black, but not agglutinated foraminifera were also present in the charcoalised, indicating a low degree of thermal samples; the foraminifer Hyperammina sp. cf. H. maturity, corresponding to the Conodont Alteration sappingtonensis Gutschick was recovered from Index of 1 determined by Burrett (1984) . sample PH-85-29 from the Sanctuary Bay section The chitinozoan species recovered from Tasmania (Bell and Winchester-Seeto 1999 in press). The include those with representatives in western 17------- Early Devonian chitinozoans from Tasmania 165 Q) en CO .0 c Q) § o ~ :.::; .8~ CO Q) CO en a. E E en ....0 o CO lE LL Cl) Q) ::: 11 11 11 11 11 11 c 11 11 00. 11 11 D :::J 11 .... 0 120m - o .... 11 (!)(!) 11 11 11 11 11 11 11 100m >< I- Fault 26 c 80m - o + o 27 E <5 60m - LL 28 en 42, 43 .0 29 • • .0 I +- 40m - C ~ 30 • • • • • • • 20m - 41 Fault <.9 0... ..J LPG - Lower Parmeener Group ~ Interbedded Coralline ~ Dolomite ~ and Shelly Limestone :.:.:=: ~ ••••••• Limestone ••••••• Pebble Conglomerate Figure 2 Stratigraphic chart of the Sanctuary Bay section, showing stratigraphic position of chitinozoan samples and distribution of species recovered. France, Bohemia, Poland, Victoria and northern Eognathodus slllcatlls sulcatus reported by Philip and Queensland, confirming the wide geographic Pedder (1968). The conodonts were extracted from spread of many important Early Devonian species.. samples PH-8S-30 (0. remscheidensis ssp. cf. O. r. Carey and Berry (1988) extracted a conodont remscheidensis, OlllodllS sp.) and PH-8S-42 (0. fauna including Ozarkodina remscheidensis ssp. cf. O. remscheidensis ssp. cf. O. r. remscheidensis) from the r. remsclleidensis (Ziegler) (figure 7A-H), Belodella Sanctuary Bay section, and samples PH-8S-33 (0. resima (Philip) (figure 7L), Oulodus sp.(figure 7J-K) remscheidensis ssp. cf. O. r. remscheidensis, B. resima) and PanderOllS ImicostatLls (Branson and Mehl) PH-85-34 (P. lInicostatlls) and PH-85-35 (0. (figure 7M-P), illustrated herein for the first time. remscheidensis ssp. cf. O. r. remscheidensis, Olllodlls None of these species, however, gives a precise age sp., P. lInicostatLls) from the 'Clearwater Point' as does the recovery of the index species, section. 166 T. Winchester-Seeto, S.P. Carey « co ~ ci. ci. Cl) Cl) Q) c.. <tl .c::<tl E .S: .0:::: en('0 ~ ~ 8, 8, c:: c:: q;: q;: Q. 36 :::J Q 80rn - 0 c 0 U... ~ 60rn - X ---· .- 35 •••••••• c · 0 -- --. 40rn - -- -- =0 --· -- ...E -- - - 0 · u.. - -·-- Cl) --- - .0 -· - 34 .0 -· - 20rn - I: ----· c - ---· -~ ---· - -·--- - ---· Fault en co u CBS - Clearwater Bay Sandstone Interbedded gumestone m Coralline and I:mm:m\ Sandstone ~ Shelly Limestone ....... Figure 3 Stratigraphic chart of the 'Clearwater Point' section, showing stratigraphic position of chitinozoan samples and distribution of species recovered. BIOSTRATIGRAPHIC IMPLICATIONS sulcatus conodont zones, and the Coopers Creek Pragian chitinozoans have been studied in only Limestone includes the boundary between the three places in Australia: Martins Well Limestone in sulcatus-kindlei conodont zones. Elsewhere Pragian northern Queensland (Winchester-Seeto 1993a), the chitinozoans are known from North Africa Coopers Creek Limestone at Boola Quarry in (Magloire 1967; Taugourdeau and de Jekhowsky eastern Victoria (Winchester-Seeto 1993a), and the 1960), southwestern Europe (Diez and Cramer 1978; Garra Formation in central New South Wales Paris 1981), central Europe (Chlup,lc et al. 1985; (Winchester-Seeto 1993b). The Garra Formation and Wrona 1980), China (Gao 1986) and Canada (Achab Martins Well Limestone both span the pesavis- et al. 1997). ..,-------- Early Devonian chitinozoans from Tasmania 167 Paris

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