Possible freshwater dinoflagellate cysts and colonial algae from the Upper Jurassic strata of the Surat Basin, Australia

ABSTRACT

Jurassic sedimentary successions in eastern Australia are widely thought to have been deposited in nonmarine environments. Thus, the discovery of low-diversity dinoflagellate cyst assemblages with associated colonial algae in the Walloon Coal Measures of the western Surat Basin provides new evidence of either a short-lived marine transgression or the very rare occurrence of nonmarine dinoflagellate cysts in pre-Cretaceous strata. Their small size, thin walls and simple proximate shapes are typical of freshwater to brackish dinoflagellate cysts, as are the low species richness and high dominance nature of the assemblages. Two new species of dinoflagellate cysts (Moorodinium crispa sp. nov. and Skuadinium fusum sp. nov.) and a new species of colonial algae (Palambages pariunta sp. nov.) are described from these assemblages. Tidal channel and tidal mudflat facies associated with these assemblages provide evidence of a possible upper estuarine setting. Support for a marine incursion is provided by U–Pb dating. This yielded an age of 150.11 ± 0.04 Ma (∼100 m above the dinoflagellate cyst assemblage in the Indy 3 well) that ties to an episode of high eustatic sea level during the Tithonian. Thus, a marine transgressive event during the Tithonian may have allowed dinoflagellates to migrate into the interior of the Australian continent. If these dinoflagellate cysts are found more widely, rather than being just an isolated occurrence in this well, they may provide a useful correlative tool for tracing distinctive brackish to marginal marine flooding surfaces in continental successions in eastern Australia.

KEYWORDS:

• freshwater dinoflagellate cysts
• Moorodinium crispa
• Skuadinium fusum
• Palambages pariunta
• estuarine
• Surat Basin
• Upper Jurassic

Acknowledgments

Carmine Wainman received a PhD scholarship from the University of Adelaide that covered most of the travel and analytical costs. We thank Cory MacNeill and Senex Energy for making the Indy 3 well available for analysis. We are grateful to John Backhouse for his assistance in the taxonomic identification of dinoflagellate cysts for this study. We also thank Jim Crowley, Debra Pierce and Alexandra Edwards from Boise State University, who assisted with mineral separation, preparation and the dating of zircon grains using CA-TIMS.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Notes on contributors

Carmine C. Wainman

CARMINE WAINMAN is a postdoctoral fellow at the University of Adelaide in Australia. He completed his PhD in 2018 at the same university. Previously he worked for the RSK Group and Woodside Energy. He received his MSci (integrated) in geology from the University of Southampton, United Kingdom. His research focuses on understanding Middle to Upper Jurassic coal-bearing strata in eastern Australia, and their correlation and stratigraphical distribution, using a multidisplinary approach.

Daniel J. Mantle

DANIEL MANTLE is a consultant palynologist/director at MGPalaeo in Perth, Western Australia, where his work has focussed on Permian–Cretaceous successions of Australia and Papua New Guinea. Daniel has a particular interest in Upper Triassic and Middle Jurassic dinoflagellate cysts and is an associate PhD supervisor for students at The University of Western Australia and The University of Wollongong. He earned his BSc degree in geology from Trinity College, Dublin and his PhD from The University of Queensland under the guidance of Prof. Geoffrey Playford and Dr Robin Helby.

Carey Hannaford

CAREY HANNAFORD is a consultant palynologist/director at MGPalaeo in Adelaide, South Australia. She completed a Ba. App. Sci (applied geology) at the University of South Australia in 1997 and began her career as a petroleum geologist at Santos Ltd, specialising in seismic interpretation and other geophysical methods. In 2004 she turned her attentions to palynology and was trained in-house by Drs Jeff Goodall, Geoff Wood and Robin Helby. Her main areas of interest include Mesozoic and Cenozoic dinoflagellate cysts, and using her palynological expertise to interpret the sequence stratigraphy of the North West Shelf of Australia.

Peter J. McCabe

PETER MCCABE is the South Australian State Chair in Petroleum Geoscience and Head of the Australian School of Petroleum, University of Adelaide. Peter obtained his PhD at the University of Keele and has more than 40 years’ experience in research organisations in North America and Australia. He is a former president of the SEPM Society for Sedimentary Geology and the American Geosciences Institute.