Guzhangian (late middle Cambrian) agnostoids and trilobites from Riana, northwestern Tasmania, Australia

A new species of trilobite, Pianaspis(?) leveni, is described from the Radfords Creek Group, Dial Range Trough, north-western Tasmania. Its age is late Middle Cambrian, either of the Lejopyge laevigata II Zone, or the L. laevigata III Zone.

Guzhangian (late Middle Cambrian) agnostoids and trilobites are described from the Belvoir Road area, western Tasmania. The fauna comprises seven agnostoid species and six trilobite species. The specimen described here as Lisogoragnostus sp. may represent a new species. The trilobites include Conocoryphidae gen. et sp. indet., which probably represents a new genus. The age of the fauna is suggested to be within the Lejopyge laevigata Zone and possibly within the Lejopyge laevigata II Zone. This indicates that the fauna is the youngest known within the economically significant Mount Read Volcanics. James B. Jago* [jim.jago@adelaide.edu.au], Adelaide University, Mawson Lakes, South Australia 5095, Australia; Christopher J. Bentley [bigfossil@bigpond.com], 30 Albert Street, Clare, South Australia 5453, Australia; Keith D. Corbett [keith.corbett@bigpond.com], 35 Pillinger Drive, Fern Tree, Tasmania 7054, Australia.

A Cambrian Series 3 (Guzhangian, Boomerangian) fauna is described from Core 12 of the Gidgealpa 1 drillhole from the Warburton Basin, northeastern South Australia. There are four agnostoid taxa: Ammagnostus laiwuensis, Lejopyge calva, L. armata and an unassigned pygidium, and six polymerid trilobite taxa: Fuchouia sp., Dorypyge sp., Solenoparia changi sp. nov., Pianaspis sp., an unassigned cranidium and an unassigned pygidium. This fauna suggests a correlation with the Goniagnostus nathorsti Zone or the lower part of the Lejopyge laevigata Zone (Boomerangian on the northern Australian biostratigraphic scheme), with the latter preferred. These are the first published descriptions of fossils of this age from the Warburton Basin. Xiaowen Sun [Xiaowen_s@yahoo.com.au], Sun Petroleum Geoservices, 4 Jolie Grove, Box Hill, Victoria 3128, Australia; Christopher J. Bentley [ bigfossil@bigpond.com], 30 Albert Street, Clare, South Australia, 5453, Australia; James B. Jago [jim.jago@unisa.edu.au], University of South Australia–STEM, Mawson Lakes, South Australia 5095, Australia.

Provincialism of the late Middle through middle Late Cambrian paraconodonts and protoconodonts

Near Middlesex Road, 9 km northeast of the Hellyer mine, northwestern Tasmania, a mineral exploration hole intersects a polymict volcaniclastic conglomerate of the Southwell Subgroup of the Mt Read Volcanics. At depths of 353 m and 364 m, fossiliferous limestone clasts within this conglomerate contain trilobites, including an unassigned agnostoid cephalon, Amphoton sp., Liopeishania sp., Menocephalites(?) sp., Lisania(?) sp. and an unassigned member of the Dorypygidae, thus suggesting an age of Goniagnostus nathorsti Zone to early Lejopyge laevigata Zone (i.e. Late Middle Cambrian) range. This shallow-water fauna is unusual for the Tasmanian Cambrian, in which most faunas are found in deeper water shales and siltstones. The horizon from which the fossils come is stratigraphically dose to a rhyolite with a SHRIMP zircon age of 503.2 ± 3.8 Ma; the usefulness of this figure in terms of the Cambrian time-scale is questioned.

A late Middle Cambrian (Ptychagnostus) punctuosus or P. nathorsti Zone) fauna occurs in the Que River Beds, Western Tasmania. Hydroids, dendroids and a possible aglaspid have been described previously. The remaining fauna of ten species of agnostid trilobites, one species of acrotretid brachiopod, various sponge spicules and one bradoriid specimen is described herein. The fauna is unusual in that no polymerid trilobites are known and that there is a very high percentage of complete agnostid specimens. One new agnostid species Ptychagnostus (?) murchisoni is described. One probable new agnostid genus and one probable new species of Diplagnostus are left in open nomenclature, because of their poor preservation.

Multivariate techniques show a strong relationship between trilobite species and lithofacies of the Holm Dai Formation. Presence-absence data on 58 species of trilobites, including 43 polymeroids and 15 agnostoids, were analyzed. Q-mode cluster analysis produced three lithologically homogeneous groups of samples: lime grainstones from Peary Land, lime mudstones from Freuchen Land, and lime mudstones from Peary Land. Nonmetric multidimensional scaling supports the reliability of the Q-mode groups, and stepwise discriminant function analysis indicates that lithology can be discriminated using a four-variable model of Catillicephala rotunda, Hemirhodon sp., Marjumia brevifrons, and Modocia planata. R-mode cluster analysis produced four groups of species: grainstone species, Peary Land mudstone species, Freuchen Land mudstone species, and agnostoid species present in all lithofacies. The intersections of Q-mode and R-mode clusters define lithofacies-related faunal associations. These techniques also call attention to samples with unusual faunal compositions and species with unusual distributions.
 The distribution of most agnostoids differs from that of most polymeroids, supporting the conclusion that agnostoids were adapted to a different mode of life from that of polymeroids. The distribution of agnostoids was probably controlled by physical and chemical factors that were not dependent on bottom sediment or conditions.

A coherent set of timing constraints is produced for Tasmania's Proterozoic and Cambrian geology when only mineral ages are considered and whole‐rock ages excluded. The oldest recognised event is the formation of sedimentary deposits which contain detrital zircons that indirectly indicate a depositional age younger than 1180 Ma. Partial melts of these sedimentary rocks were incorporated in Neoproterozoic, Devonian and probably Cambrian felsic magmas. Neoproterozoic granite on King Island has an age of 760 ± 12 Ma and is part of a high‐level intrusive episode that accompanied the Wickham Orogeny, an event with regionally varied strain that is represented in northwestern Tasmania by a low‐angle unconformity, by altered granitoid with a magmatic age of 777 ± 7 Ma, and by the thick turbidite pile of the Burnie and Oonah Formations with its syndepositional intrusions of Cooee Dolerite. The late Neoproterozoic was relatively quiet tectonically but by early in the Middle Cambrian a crustal collision which marked the early phase of the Tyennan Orogeny brought about high‐level emplacement of ultramafic‐bearing allochthons and deep‐seated metamorphism of quartzose sedimentary and basaltic rocks. The ultramafic allochthons carried tonalite that had crystallised only shortly before at 510 ± 6 Ma, while the deep‐seated metamorphism produced eclogite at 502 ± 8 Ma. By middle Middle Cambrian times the metamorphic rocks had been uplifted and they experienced repeated uplift during the period of Mt Read volcanism and onward to the close of the Tyennan Orogeny in the Early Ordovician, an overall period of some 20 million years from the early Middle Cambrian. Regionally varied strain was again a feature during the Tyennan Orogeny, with the Smithton area in northwestern Tasmania and King Island occupying relatively undeformed cratonic positions.

An unusually diverse trilobite fauna in the Holm Dai Formation is dominated by polymeroid genera and species that are most characteristic of the lower and middle Cedaria Zone as widely applied in North America. Several agnostoid species are characteristic of the upper Lejopyge laevigata Interval-zone of Robison (1984), and correlation with the Swedish standard for north-western Europe indicates a late Middle Cambrian age. Biogeographic analysis shows that continental endemism of the 34 polymeroid genera and 43 polymeroid species in the Holm Dal Formation exceeds 88 and 97percent respectively. In marked contrast, all 12 of the Holm Dal agnostoid genera and at least 13 of the 15 agnostoid species have intercontinental distributions (0 and 13 percent endemism respectively). Comparisons with coeval North American faunas suggest that Middle Cambrian biozones based on polymeroid species may be useful on a regional scale, but probably will not be applicable on a continental scale. Genus-based polymeroid zones may be applicable on a continental scale, but long stratigraphic ranges of genera will limit precision. Species-based agnostoid zones will be applicable globally, but probably will be most useful in deposits representing the neritic to oceanic transition. Fifty-eight trilobite species, some in open nomenclature, are described from Peary Land and Freuchen Land. Of the taxa represented, 9 of 34 genera are new: Balderia, Conopolus, Durinia, Holmdalia, Pearylandia, Tavsenia, Toragnostus, Verditerrina, and Wandelella. Twenty-four species are new: Balderia aspera, Blountia bella, Bolaspidella stymacantha, Cedaria major, Cedaria tumicephala, Conopolus granulus, Crepicephalus eos, Durinia granulosa, Elrathia omega, Glaphyraspis alpha, Madarocephalus scolus, Marjumia brevifrons, Marjumia spinosa, Matania matuta, Matania quadrata, Modocia planata, Nixonella furta, Olenoides ternus, Onchonotopsis physala, Pearylandia parva, Syspacheilus catatate, Tavsenia ditrema, Verditerrina lacinia,and Wandelella compta. In addition, the new species Conopolus rasettii is described from Quebec, Canada. A lectotype is designated for Proagnostus bulbus Butts 1926, the type species of Proagnostus.

Ten species of agnostid trilobites, including a new species, Utagnostus(?) nevel, are described from two localities within the lower sedimentary succession of the Radfords Creek Group, Dial Range Trough, north-western Tasmania. The faunas from both localities (near Gunns Plains) are of late Middle Cambrian age; one is either of the Lejopyge laevigata II Zone or the L. laevigata III Zone and the other is either of the L. laevigata III Zone or the Damesella torosa-Acsionepea janitrix Zone.

Jago, J.B., Bentley, C.J., Laurie, J.R. & Corbett, K.B., 26 June 2018. Some middle and late Cambrian trilobites and brachiopods from the Adamsfield Trough, Tasmania. Alcheringa 43, 1-17. ISSN 0311-5518.Cambrian Series 3 and Furongian trilobites and brachiopods are described from the Adamsfield Trough in southwestern Tasmania. The oldest fossils are very poorly preserved trilobites, assigned to Asaphiscidae gen. et sp. indet. from within the Island Road Formation a short distance above the unconformity with the underlying Proterozoic Wedge River Beds. A trilobite species from within the isolated Boyd River Formation is referred to Lioparia sp. The Island Road Formation and the Boyd River Formation are stratigraphically equivalent to the Trial Ridge Beds which have previously been dated as belonging to the Lejopyge laevigata Zone. The Trial Ridge Beds are overlain unconformably by the Singing Creek Formation. In the Adamsfield, Clear Hill and Stepped Hills areas, stratigraphic equivalents of the Singing Creek Formation collectively contain the trilobites Pseudaphelaspis sp., Pseudaphelaspis? sp., Prochuangia sp., Mindycrusta sp., Nepeidae gen. et sp. indet., and Olenidae gen. et sp. indet. plus the brachiopods described herein as Billingsella sp. aff. costata, Billingsella sp. A, Billingsella sp. B and a possible member of the Billingselloidea. The Singing Creek Formation has been previously correlated with the Stigmatoa diloma Zone. The genus Lotosoides Shergold 1975 is placed in synonymy with Prochuangia Kobayashi 1935.James B. Jago* [jim.jago@unisa.edu.au] University of South Australia, School of Natural and Built Environment, Mawson Lakes, SA 5095, Australia; Christopher J. Bentley [bigfossil@bigpond.com] 30 Albert Street, Clare, SA 5453, Australia; John R. Laurie [john.r.laurie@gmail.com] Department of Biological Sciences, Macquarie University, NSW 2109, Australia; Keith D. Corbett [keith.corbett@bigpond.com] 35 Pillinger Drive, Fern Tree, Tas 7054, Australia.

The Cambrian–Ordovician transition of the western Mediterranean region (NW Gondwana) is characterized by the record of major erosive unconformities with gaps that range from a chronostratigraphic stage to a series. The hiatii are diachronous and involved progressively younger strata along the Gondwanan margin, from SW (Morocco) to NE (Montagne Noire). They can be related to development of a multi-stage rifting (further North), currently connected to the opening of the Rheic Ocean, and concomitant erosion on southern rift shoulders. The platforms of this margin of Gondwana occupied temperate-water, mid latitudes and were dominated by siliciclastic sedimentation, while carbonate factories were only episodically active in the Montagne-Noire platform. The Upper Cambrian is devoid of significant gaps in the southern Montagne Noire and the Iberian Chains. There, the sedimentation took place in a transgressive-dominated depositional system, with common offshore deposits and clayey substrates, and was bracketed by two major regressive trends. The Late Cambrian is also associated with the record of volcanic activity ( e.g., in the Cantabrian and Ossa-Morena zones, and the northern Montagne Noire), and widespread development of a tectonic instability that led to the episodic establishment of palaeotopographies and record of slope-related facies associations. Several immigration events are recognized throughout the latest Middle Cambrian, Late Cambrian and Tremadocian. The trilobites show a stepwise replacement of Acado-Baltic-type families ( e.g., the conocoryphid–paradoxidid–solenopleurid assemblage) characterized by: (i) a late Languedocian (latest Middle Cambrian) co-occurrence of Middle Cambrian trilobite families with the first anomocarid, dorypygid and proasaphiscid invaders; (ii) a Late Cambrian immigration replacing previous faunas, composed of trilobites (aphelaspidids, catillicephalids, ceratopygids, damesellids, eulomids, idahoiids, linchakephalids, lisariids, onchonotinids, and pagodiids), linguliformean brachiopods (acrotretids, obolids, scaphelasmatids, siphonotretids, and zhanatellids), echinoderms (mitrates, glyptocystitid cystoids, and stromatocystoids), and conodonts belonging to the lower Peltura Zone; and (iii) the subsequent input of new trilobites (asaphids, calymenids, catillicephalids, nileids and remopleurids), which marks the base of the Proteuloma geinitzi Zone, associated with pelmatozoan holdfasts ( Oryctoconus), and a distinct input of late Tremadocian conodonts ( Paltodus deltifer Zone). The biogeographic distribution of latest Middle and Late Cambrian trilobites supports brachiopod data indicating strong affinities between the western Mediterranean region, East Gondwana (North China/Korea, South China, Australia, and Antarctica) and Kazakhstania during the late Languedocian, which became significantly stronger during the Late Cambrian. This major shift may suggest modification in oceanic circulation patterns throughout Gondwana across the Middle–Late Cambrian transition.

The chronostratigraphical scale is a hierarchical scheme that is subdivided into increasingly smaller units, from eonothem down to the level of the substage and beyond. Boundaries of chronostratigraphic intervals typically coincide with individual bioevents. As these intervals become smaller, their geographic utility tends to shrink. Typically, where the original interval is inapplicable, the next highest interval in the scale is used for communication. Where appropriate intervals are unavailable, confusion reigns. A stadial subdivision of the Australian mid–late Cambrian (equivalent to the international Miaolingian and Furongian series) was completed in 1993 with the definition of the Furongian Iverian Stage. One stage, the Ordian, was initially suggested as the lowest stage for what is now the Miaolingian, but should be considered to belong to upper Series 2 of the Cambrian. No older Cambrian stages have been proposed in Australia. Indeed, the base of the Ordian has not been defined, due in part to the incompleteness of Series 2 successions in central and northern Australia. A longstanding impediment to the establishment of lower Cambrian stages in Australia arises from the fact that the entire Australian stadial scheme for the Miaolingian and Furongian series was established in the cratonic basins of central-northern Australia, whereas the lower Cambrian is best developed in separate South Australian basins. With the rapid increase in knowledge of the biostratigraphic successions in the South Australian lower Cambrian (Terreneuvian and Series 2) over the last three decades, the time seems ripe for the establishment of such a stadial subdivision. This will require careful correlation between the mostly Terreneuvian and Series 2 succession in South Australia and the mostly Miaolingian–Furongian succession in central and northern Australia. Taxa that can be used for such a stadial subdivision include trilobites, organophosphatic brachiopods, archaeocyaths, small shelly fossils, molluscs and acritarchs, as each has provided the basis of zonations in the South Australian successions. John R. Laurie [john.r.laurie@gmail.com], Geoscience Australia, Symonston Australian Capital Territory 2601, Australia, and School of Natural Sciences, Macquarie University, North Ryde, New South Wales 2109, Australia. Peter D. Kruse [archaeo.kruse@gmail.com], South Australian Museum, Adelaide South Australia 5000, Australia. Glen A. Brock [glenn.brock@mq.edu.au], School of Natural Sciences, Macquarie University, North Ryde, New South Wales 2109, Australia. James D. Holmes [jamesholmes83@gmail.com], Palaeoscience Research Centre, University of New England, Armidale New South Wales 2351, Australia. James B. Jago [Jim.Jago@unisa.edu.au], University of South Australia-STEM, Mawson Lakes, SA 5095, Australia, and South Australian Museum, Adelaide, South Australia 5000, Australia. Marissa J. Betts [Marissa.Betts@une.edu.au], Palaeoscience Research Centre/LLUNE, University of New England, Armidale New South Wales 2351, Australia. John R. Paterson [jpater20@une.edu.au], Palaeoscience Research Centre, University of New England, Armidale New South Wales 2351, Australia. Patrick M. Smith [Patrick.Smith@austmus.gov.au], Australian Museum Research Institute, Sydney New South Wales 2010, Australia, and School of Natural Sciences, Macquarie University, North Ryde New South Wales 2109, Australia.

A review of the Cambrian biostratigraphy of South Australia

A small, but diverse fauna of molluscs is described from the lower beds of the Holm Dal Formation (late Middle Cambrian) of central North Greenland. Species of Helcionellacea and Hypseloconellacea dominate, although only individuals of the former superfamily are numerically common, as are examples of a single stenothecoid species. Paragastropoda and Hyolitha are rare faunal elements. A single newgenus (Perssuakiella) and 5 new species are described: P. troelseni, Latouchella holmdalense, L. pearylandica, Stenothecoides groenlandica and Costipelagiella kochi.