Barry D. Webby

History of the Ordovician continental platform shelf margin of Australia

Abstract Much of South Australia, western New South Wales, and Tasmania was affected by the Late Cambrian‐Early Ordovician Delamerian Orogeny. Areas of the former shelf margin exhibit molasse‐type conglomerates overlying a major late Middle to Late Cambrian unconformity (Jukesian Movement in Tasmania or Mootwingee Movement in western N.S.W.). In continental platform areas to the north the effects of the orogeny were less intense with, in the Georgina Basin for instance, only dis‐conformable relationships, and the overlying deposits consisting of fine elastics and carbonates. Regression accompanied this first phase of tectonic upheaval and was followed by a period of ‘late Tremadoc’ transgression of the sea into several embayment areas of the continental platform. This short‐lived transgression was succeeded by ‘early Arenig’ regression which appears to be related to a second, less intense Delamerian orogenic phase. Expression of this phase ranges from unconformity in west Tasmania (Haulage and Lynchford M...

Stratigraphy and regional setting of the Cliefden Caves limestone group (Late Ordovician), central‐western New South Wales

Abstract The 460 m‐thick Cliefden Caves Limestone Group is the oldest and best exposed, extensive body of limestone in N.S.W. Its Late Ordovician faunas and floras are comparatively well preserved and it has some excellent silicified horizons, especially in the upper part of the sequence. In the nominal type area at Cliefden Caves, the limestone has been subdivided into three formations—the Fossil Hill Limestone (lower), the Belubula Limestone (middle) and the Vandon Limestone (upper). Only the Belubula Limestone remains undifferentiated. The Fossil Hill Limestone has been further subdivided into six members (Gleesons, Kalimna, Wyoming, Taplow, Dunhill Bluff and Transmission Limestone Members, respectively), and the Vandon Limestone into two members (Trilobite Hill and Mount Lewin Limestone Members). Each of these subdivisions is defined herein, with a designated type section and a description of its content and distribution. In late Gisbornian to early‐middle Eastonian time, the Cliefden Caves Limestone ...

Devonian geological history of the Lachlan Geosyncline

Abstract The principal Lower Devonian depositional belts of the Lachlan Geosyncline were a western, predominantly non‐volcanic belt, including the Cobar Basin and the Melbourne Trough with its southerly extension into Tasmania, and an eastern, volcanic belt, including the Parkes Platform, Cowra Trough, Molong Rise, Hill End Trough and Capertee Rise. These were separated by a more or less continuous median stabilized block comprising the Girilambone Arch, Wagga Arch and Snowy Mountains Block, which acted as a mildly positive structure during Early Devonian time. The sea regressed from the Cobar Basin and Melbourne Trough in about late Emsian times. Succeeding Devonian deposits in the western belt were entirely of non‐marine type. The Middle Devonian Tabberabberan Orogeny was responsible for the virtual stabilization of the entire geosynclinal tract, for the main uplift, folding and faulting of the Hill End Trough and adjacent rises, and folding in the Melbourne Trough. Non‐marine basin and platform deposit...

Precambrian‐Cambrian trace fossils from western New South Wales

The distribution of trace fossils in the upper part of the Adelaidean succession (Farnell Group) of the Barrier Range near Fowlers Gap is reviewed. Of the main, stratigraphically distinct assemblages, the older from the Fowlers Gap Formation, contains only a few, simple, non‐diagnostic, sinuous and branching trails, and is assumed to be of latest Precambrian age. The assemblage in the succeeding Lintiss Vale Formation has a high diversity, mainly of simple behavioural types produced by worm‐like animals and molluscs, but lacking arthropod traces. It therefore represents a latest Precambrian or an earliest Cambrian assemblage. A third ichnofauna with simple, sinuous and branching trails is recorded from the Wonominta Beds of the Warratta inlier west of Tibooburra. The occurrence of these trails indicates that at least in the northern areas of ‘basement’ Wonominta outcrop the rocks are no older than latest Precambrian (i.e. the age of the earliest indubitable traces of animal activity) and, judging from the...

Ordovician sphinctozoan sponges from central New South Wales

Sphinctozoan sponges are described and illustrated for the first time from Late Ordovician sequences, from the Belubula Limestone and the Angullong Tuff of the Cliefden Caves area, central New South Wales. The occurrences help to bridge the gap in the record between earliest known, Middle Cambrian, and later, Early Devonian, forms reported recently from other New South Wales localities. The sphinctozoans appear to have had a restricted distribution in their Early Palaeozoic history, mainly confined to island-arc shelf areas of eastern Australia and possibly similar settings of the Palaeo-Pacific rim in western North America. The new genus and species, Belubulaia packhami, is described from silicified material in the lower part of the Belubula Limestone near Little Boonderoo and Licking Hole Creek. A second new genus and species, Angullongia vesica, is much larger, calcareous and from an unnamed thin limestone unit of the Angullong Tuff on the property of Millamolong. Together these new genera constitute t...

Late Ordovician nautiloids from central New South Wales, Australia

Nine nautiloid taxa are described from the Late Ordovician sequences (Caradoc-early Ashgill equivalents) of central New South Wales, and include Trocholites costatus sp. nov., Paradiscoceras dissitum sp. nov., Cliefdenoceras gregarium gen. et sp. nov. and Troedssonella sp. The nautiloid fauna occurs chiefly in shallow-water sediments on offshore highs (Parkes Platform and Molong High near Parkes and Orange) of the main volcanic arc in the Tasmanides. This island arc fauna is dominated by nektonic forms. It lacks definite nekto-benthonic forms presumably because deep waters around the highs acted as a barrier to their migration. All taxa except C. gregarium are relatively long ranging and geographically widespread. The presence of Troedssonella in the Fossil Hill Limestone suggests a Llandeilian to early Caradocian age. The fauna is broadly similar to that of the Siberian Platform, Kazakhstan and China, although most elements are cosmopolitan or nearly so. The contemporaneous Tasmanian nautiloid fauna is s...

Ordovician stromatoporoids from the Langkawi Islands, Malaysia

Four species of labechiid stromatoporoids are described from Unit J of the Lower Setul Limestone (Middle Ordovician) of the Langkawi Islands. They include Labechia variabilis Yabe & Sugiyama 1930 and Rosenella woyuensis Ozaki 1938, reported previously from the Middle Ordovician of north China and the Gisbornian-Eastonian of New South Wales. Tentative correlations employing nautiloids and conodonts suggest that the Malaysian and perhaps some of the north Chinese labechiid occurrences have a pre-Chazyan Whiterockian (Llanvirnian) age, that is, they are the oldest known Ordovician stromatoporoids, appearing prior to the previously earliest known Chazyan forms of North America and Tasmania.

Ordovician stromatoporoids from Tasmania

Stromatoporoids are important and conspicuous constituents of the Ordovician limestones of the Gordon Group in Tasmania. The fossils occur through much of the succession, from the Cashions Creek Limestone and equivalents upwards, and from many different localities through west-central and northern Tasmania. A total of 16 species (6 new) of the Order Labechiida are described and illustrated from the sequences. They include the new species Stylostroma ugbrookense, S. bubsense, Aulacera denensis, A. gunnensis, Thamnobeatricea gouldi and T.? vesiculosa. The fauna also comprises representatives of Labechia, Stromatocerium, Labechiella, Pachystylostroma, Rosenella, Pseudostylodictyon, Cystostroma and Alleynodictyon. A number of cyanobacterial associations are also described, including occurrences of Labechiella variabilis with its normal pillars colonized by Cliefdenia-like clusters, and Cystostroma involved in sheet-like intergrowths with an unnamed cyanobacterium resembling Epiphyton. In general the stromatop...

Lower Devonian stromatoporoids from the Jesse Limestone of the Limekilns area, New South Wales

An assemblage of well preserved Devonian stromatoporoids is described from the Jesse Limestone of the Limekilns area, central-western New South Wales. The fauna, which comes from limestone breccia deposits of the western, Diamond Creek occurrence, is interpreted as having an allochthonous origin. Eleven species of stromatoporoids are described and illustrated including representatives of Actinostroma, Gerronostroma, Schistodictyon, Amnestostroma, Pseudotrupetostroma, Salairella, Stromatopora, Atopostroma, and Habrostroma. Details of stromatoporoid microstructure of well preserved specimens of Amnestostroma and Pseudotrupetostroma are also presented for the first time. The descriptions of new species include, Gerronostroma vergens, Amnestostroma crassum, Pseudotrupetostroma jessiense and P. ripperae. Other elements of the Jesse fauna comprise occurrences of Siberian, South Chinese and Canadian affinity, which suggests probable zoogeographic links with these regions. The Jesse Limestone has been interpreted...

The oldest Ordovician stromatoporoids from Australia

The oldest known Australian Ordovician stromatoporoids are described from the Cashions Creek Limestone (formerly the Maclurites-Girvanella horizon) and correlatives of the Gordon Subgroup in Tasmania. The Cashions Creek Limestone and equivalents are correlated approximately with the North American Chazyan (Middle Ordovician). Representatives of Labechia, Stratodictyon and Stromatocerium are recorded from localities in the Mole Creek area, from the Florentine Valley and from Melrose. Three new species, Labechia banksi, Stratodictyon vetus and Stromatocerium bigsbyi are described. L. banksi comes from a slightly higher horizon in the succession at Mole Creek where it occurs in association with the earliest corals (Lichenaria). The distribution of the earliest Ordovician stromatoporoids — those appearing in the North American and Tasmanian successions — is reviewed, together with a discussion of their possible origins and interrelationships.