Upper Ordovician trilobites from central New South Wales

Twelve trilobite species are described and illustrated from Upper Ordovician (Caradoc) successions of central New South Wales, Included among the forms is a new scutelluid genus, Heptabronteus, with two new species, H. atavus (type species) and H. major, and five other new species, Toemquistia arguta, Parkesolithus dictyotos, Sphaerocoryphe exserta, AmphiHchas nasutus, and A. encyrtos.A discussion of relationships between Heptabronteus and other scutelluid genera is presented.Triarthrus is recorded for the first time from New South Wales, and evidence for dimorphism in the raphiophorid, Malongullia oepiki Webby, Moors, and McLean, 1970, considered.The stratigraphical distribution of the faunas is described, and zoogeographical relationships discussed.The New South Wales fauna is included in the Heptabronteus-Pliomerina province of Australia, South-East Asia, and Kazakhstan.one of two or more separate provinces within the much larger, band-like, probably equatorial, Remopleuridid realm of the Caradoc.The faunas are interpreted broadly as occurring in an island-arc tectono-environmental setting.They have been differentiated into a possible benthonic assemblage in the shallow-water carbonate rise facies, and into inferred benthonic and pelagic associations in the deeper, graptolitic shale slope and trough facies.Earlier descriptions of the Upper Ordovician trilobites from central New South Wales were given by Webby, Moors, and McLean (1970), Campbell and Durham (1970), Webby (1971), and Webby (1973).This paper concludes the description of the faunas based on collections in the Department of Geology and Geophysics, University of Sydney. DISTRIBUTIONThe distribution of trilobites in the Upper Ordovician successions of central New South Wales is represented in text-fig.1. Locality details are given in previous papers and in the systematic descriptions of these pages.Most of the localities occur within the areas of the geotectonic 'highs', the Molong Rise and the Parkes Platform (textfigs.2 and 4), in off-shore parts of the Lachlan Geosyncline (Packham 1969).In both regions extensive outpourings of Lower or Middle Ordovician andesitic volcanics accumulated on the sea floor, and seem to have built up 'highs' within the geosyncline.These volcanic piles apparently became emergent and planated, providing platforms for the deposition of shallow-water carbonates.It remains to be established whether in the Upper Ordovician a deeper-water shale succession was being deposited in the Cowra Trough between contemporaneous limestone successions of the Parkes Platform and Molong Rise, or whether the carbonates originally formed on a single, extensive Parkes-Molong volcanic rise (text-fig.4).Packham (1967; 1969, p. 217) has indicated that Upper Ordovician graptolite deposits occur in the Cowra Trough at Tomingley but, considering their location 40 miles (64 km) north of Parkes, they may not be strictly assignable to the trough.Scheibner (1972) has claimed that the Cowra Trough originated by splitting of the Parkes-Molong volcanic rise in the early Silurian.To the west of the Parkes Platform, late Ordovician quartz-rich greywackes and slates were deposited in the Wagga Trough, a possible [Palaeontology, Vol.17, Part 2, 1974, pp.203-252, pis.28-34.]A TEXT-FIG.I. Chart showing trilobite distribution in Upper Ordovician of central New South Wales.The three dimorphs in the faunas are numbered 1, 2, and 3. Relative abundances at the best collecting locality of the particular unit are given by symbols: VC, very common; c, common; me, moderately common; r, rare; vr, very rare.P.P., Parkes Platform.H.