New insights on the Upper Cretaceous Tiger Supersequence of the Bight Basin from International Ocean Discovery Hole U1512

Summary

The Bight Basin is considered to be one of Australia’s most prospective petroleum regions. However, the sparsity of geologic data means that potential petroleum plays in the basin have yet to be firmly established. In late 2017, International Ocean Discovery Program (IODP) Expedition 369 extracted 700 m of core from the Upper Cretaceous Tiger Supersequence from Site U1512 in the western Ceduna Sub-basin. The core represents the most substantial lithological dataset obtained from the basin and the first opportunity to characterise the succession. Two dinocyst zones (the Turonian Paleohystrichophora infusorides and the Coniacian Conosphaeridum striatoconum zones) assigned at this locality are consistent with shipboard nannofossil zonations. Facies analysis supports deposition by hypopycnal and hyperpycnal flows in a prodelta setting with seismic data suggesting postdepositional deformation in the upper 350 m of the succession. Palynofacies assemblages are dominated by phytoclasts that indicate close proximity to a fluvio-deltaic source. Source rock analyses reveal samples have limited total organic carbon (TOC) values (<1.52%) with little response for S1 due to the immature nature of the samples. However, other datasets suggest that the base of the hole at Site U1512 was close to intersecting potential organicrich black shales associated with Ocean Anoxic Events 2. The new data provide insights into the Tiger Supersequence in this locality and further work will help refine its character, evolution and the petroleum prospectivity of the region.

• Bight Basin
• U1512
• Tiger Supersequence
• hypopycnal flow
• hyperpycnal flow