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.