Evidence for non-marine Jurassic to earliest Cretaceous sediments in the pre-breakup section of the Mentelle Basin, southwestern Australia

Abstract

The Mentelle Basin, located off the southwestern continental Australian margin, is an under-explored deep-water basin that developed during the breakup of eastern Gondwana in the Middle Jurassic through to the Early Cretaceous. There is a high degree of uncertainty in stratigraphic interpretations of the basin owing to the lack of well and seismic data in the region. As a consequence, there has been a heavy reliance on data from the neighbouring Perth Basin to infer the geological history of the Mentelle Basin. During Expedition 369 of the International Ocean Discovery Program, a single hole was drilled with a rotary core bit to 517.10 m below seafloor at Site U1515 on the continental slope in the eastern Mentelle Basin. The aim was to sample and date the inferred Permian to Jurassic pre-breakup strata. The presence of palynomorphs including Murospora florida and Retitriletes watherooensis in the fluvio-lacustrine succession below the Valanginian breakup unconformity indicates a Jurassic to earliest Cretaceous age for the upper part of the pre-rift sedimentary succession. Notable characteristics of this succession include intervals with high percentages of total organic carbon (up to 44 wt%) and high hydrogen index values (Type I source rocks) associated with an increase in Botryococcus and other freshwater algae that accumulated in shallow lakes and waterlogged floodplains. A possible example of dinoturbation was also noted in this core. The discovery of Jurassic to earliest Cretaceous pre-breakup strata at Site U1515 suggests that Jurassic rifting was not constrained to the western depocentre of the Mentelle Basin, but also extended to a number of depocentres in the eastern Mentelle Basin. This has significant implications for the understanding of the regional tectonic history and the Mentelle Basin’s petroleum potential.

• Pre-breakup strata sampled in the eastern Mentelle Basin for the first time by IODP Expedition 369

• Upper Jurassic–Lower Cretaceous non-marine strata below the Valanginian Unconformity

• High TOC’s, high abundances of Botryococcus algae in a few horizons and a possible example of dinoturbation

• Jurassic rifting not constrained to the western Mentelle Basin, but to depocentres in the east

Keywords:

• Mentelle Basin
• Upper Jurassic
• Lower Cretaceous
• Valanginian unconformity
• fluvio-lacustrine
• eastern Gondwana
• palynology
• petroleum potential

Acknowledgements

This research used samples and/or data provided by the International Ocean Discovery Program (IODP). We thank the IODP and the Australia–New Zealand IODP Consortium (ANZIC), which enabled Carmine Wainman, Lloyd White and Alessandro Maritati to participate in Expedition 369. We thank the IODP Expedition 369 participants for their assistance during the drilling of Site U1515, the analysis of data on the JOIDES Resolution and reviewing the manuscript prior to submission. Tracy Quan and Tao Wu from Oklahoma State University, US produced a data report titled ‘Organic and carbonate isotope record from IODP Expedition 369, Site U1515, Hole A’ which the organic carbon record for this article was extracted from. This will be avaliable on the IODP-JOIDES Resolution Science Operator website (www.iodp.tamu.edu) in due course. Free-air gravity and bathymetric data used to compute the Bouguer anomaly was download from the International Gravimetric Bureau and the National Geophysical Data Center (NOAA), respectively, and processed using the Generic Mapping Tools software. MGPalaeo kindly assisted by processing samples for palynology. Stratabugs was used under licence to produce the palynological plot in the Supplementary paper. Peter McCabe and Simon Holford from the University of Adelaide’s Australian School of Petroleum also provided assistance in preparing the manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

ANZIC is supported by the Australian Government through the Australian Research Council’s LIEF funding scheme [LE160100067] and the Australian and New Zealand consortium of universities and government agencies.