The Ordovician System in Australia and New Zealand

The stratigraphic overview presented in this chapter substantially updates and revises the last major review of the Ordovician rocks of Australia and New Zealand published 40 years ago. In the western two-thirds of the present-day continent of Australia, Ordovician sedimentary rocks are restricted to intracratonic basins. The Canning Basin (Western Australia) and Amadeus Basin (central Australia) contain the best known Lower and Middle Ordovician shallow marine successions. The eastern third of the continent, known as the Tasmanides, comprises multiple orogens (i.e. Delamerian, Lachlan, New England, Thomson, Mossman) that formed along the convergent East Gondwana Margin. As a result, volcanic and intrusive rocks are much more common in these orogens than in the intracratonic basins. Their deep-water depositional environments span 31 graptolite biozones. Slope and basinal siliceous sedimentary rocks are constrained by a newly defined set of 12 conodont biozones, complementing the conodont biostratigraphic scheme refined for shallow-water environments from the basal boundary of the Ordovician to the latest Katian. In some places, these conodont biozones are integrated with radiometric ages from tuff interbeds (e.g. Canning Basin). Ordovician graptolitic strata in the Buller Terrane of New Zealand share palaeogeographic links with those in the Bendigo Zone of the western Lachlan Orogen.