Testing the Gippsland zonation in northern Australia: palynostratigraphical analysis of a 23 Ma ⁴⁰Ar/³⁹Ar dated claystone from Toowoomba, southeast Queensland

The spore-pollen zonation developed for the Gippsland Basin, southeast Australia, is widely used to date Paleogene-Neogene terrestrial sediments elsewhere in Australia. Microfloras preserved in an argon-40 ( 40Ar)/argon-39 (39Ar) dated 23 Ma claystone on the summit of the Great Dividing Range at Toowoomba in subtropical southeast Queensland indicate the Gippsland zonation, and the parallel schemata developed for the epicontinental Murray Basin in southeastern Australia provide only a general guide to the age of Late Paleogene-Neogene sediments as far north as Queensland. The finding reiterates the need to develop regional spore-pollen palynostratigraphies for Queensland (and northern Australia) centred on Cenozoic microfloras whose geologic age can be independently verified by other dating techniques. The same microfloras, however, are reliable evidence of past vegetation and climates, in this instance that a form of Nothofagus-gymnosperm temperate rainforest was colonising basaltic soils at Toowoomba during the Oligo-Miocene transition when southeast Queensland was located c. 15° south of its present latitudial position.