Utilizing U–Pb CA-TIMS dating to calibrate the Middle to Late Jurassic spore-pollen zonation of the Surat Basin, Australia to the geological time-scale

Abstract

Wainman, C.C., Hannaford, C., Mantle, D. & McCabe, P.J., April.2018. Utilizing U–Pb CA-TIMS dating to calibrate the Middle to Late Jurassic spore-pollen zonation of the Surat Basin, Australia to the geological time-scale. Alcheringa XX, xx-xx.

Spore-pollen palynostratigraphy is commonly used to subdivide and correlate Jurassic continental successions in eastern Australia and thus aid the construction of geological models for the petroleum and coal industries. However, the current spore-pollen framework has only been tenuously calibrated to the geological time-scale. Age determinations are reliant on indirect correlations of ammonite and dinoflagellate assemblages from New Zealand, the North West Shelf of Australia and Southeast Asia to the standard European stages. New uranium-lead chemical abrasion thermal ionization mass spectrometry (U–Pb CA-TIMS) dates from 19 tuff beds in the Middle–Upper Jurassic Injune Creek Group of the Surat Basin enables regional spore-pollen palynostratigraphic zones to be precisely dated for the first time. These results show the base of the APJ4.2 and APJ4.3 subzones are similar in age to previous estimates (Middle Jurassic, Bathonian) from indirect palynostratigraphic correlation. However, the base of the APJ5 Zone and the APJ6.1 Subzone may be somewhat younger than previously estimated, possibly by as much as 2.5 and 4.2 Myrs, respectively. The continued utilization of U–Pb CA-TIMS dates will further refine the absolute ages of these zones, improve the inter- and intra-basinal correlation of Middle–Upper Jurassic strata in eastern Australian basins and greatly enhance intercontinental correlations.

Carmine Christopher Wainman [[email protected]] and Peter James McCabe [peter.mccabe@adelaide,edu.au] Australian School of Petroleum, University of Adelaide, SA, 5005, Australia; Carey Hannaford [[email protected]] and Daniel Mantle [[email protected]] MGPalaeo Pty Ltd, 5 Arvida Street, Malaga, WA, 6090, WA, Australia.

Key words:

• U–Pb CA-TIMS
• tuffs
• palynostratigraphy
• Surat Basin
• Jurassic

Acknowledgements

Carmine Wainman received a PhD scholarship from the University of Adelaide that covered most of the travel and analytical costs. Geoff Wood from Santos Limited kindly provided palynological summaries and range charts for the Pleasant Hills 25 well. We thank Robert Nicoll of Geoscience Australia for reviewing the manuscript prior to submission and John Backhouse for insightful discussions regarding the identification of thin-walled brackish-marginal marine dinoflagellate cysts. Jesse Vitacca from MGPalaeo kindly assisted with palynological processing. Stratabugs was used under licence to produce the palynological plots in the appendices.