Occurrence of the ammonite Goodhallites goodhalli (J. Sowerby) in the Eromanga Basin,Queensland: an index species for the late Albian (Cretaceous)

Mortoniceratid ammonites of the Eromanga Basin of Queensland, although uncommon, are reviewed and reassessed utilising all known collections. Representatives of this group are restricted to the Allaru Formation and almost all specimens are Goodhallites goodhalli, a well-known species from the English Gault. The Allaru Formation overlies the Toolebuc Formation, widely considered to be an essentially isochronous unit because of its unusual sedimentary and geochemical character. Using G. goodhalli, the middle and upper Allaru Formation can be directly correlated with the early late Albian orbignyi and auritus Subzones of the Mortoniceras inflatum Zone as recognized in the reference ammonite zonation embedded in the standard Cretaceous time scale. Overlapping ranges of G. goodhalli and Labeceras and Myloceras allow these common Austral heteromorph genera to be also confidently assigned a late Albian age in Australia, matching their biostratigraphic occurrence in South Africa.