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

Abstract

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.

Keywords:

• Pollen/spores
• Gippsland Basin
• Murray Basin
• Paleogene-Neogene
• zonation
• Queensland
• Australia

Acknowledgments

This paper has depended on the kindness of many persons. In particular we wish to thank Ron Bathurst (Queensland Department of Transport and Main Roads, Brisbane) and Anne Riesz (Murray-Darling Basin Authority, Canberra) for alerting us to the presence of the lignitic claystone stratum in the Toowoomba Bypass Tunnel, Dan Mantle (formerly Geoscience Australia, Canberra) who arranged processing of the samples, Ben Cohen (AGES Laboratory, University of Queensland) for dating the basalts samples, Ray Carpenter (University of Adelaide, Adelaide) for examining the palynodebris for identifiable macroscopic remains, and Mary Dettmann (University of Queensland, Brisbane), Jim Riding (British Geological Survey, Keyworth) and an anonymous referee who provided valuable comments on an earlier version of this paper.

Additional information

Notes on contributors

Mike Macphail

MIKE MACPHAIL completed his PhD on the history of the postglacial vegetation and climate in Tasmania, Australia during 1975. Since then he has been a biostratigrapher for Esso Australia working on the southern margin basins. Mike was also a research fellow at several Australian and New Zealand universities whilst running a palynostratigraphical consultancy focusing on the Mesozoic and Cenozoic of Australia.

Dave Gibson

DAVE GIBSON graduated from the Australian National University, Canberra, Australia in 1972, majoring in geology. Since then he has worked for government geological agencies in Australia and Papua New Guinea, most recently Geoscience Australia, specialising in regional geological mapping, sedimentary geology, regolith, geomorphology and groundwater. Dave retired in 2013.