New insights on Upper Cretaceous stratigraphy and sedimentology of the Bight Basin, Australia from IODP Site U1512

Abstract

The Bight Basin, on Australia’s southern margin, is one of the world's most prospective deepwater frontier basins. The 10 offshore wells drilled in the basin had limited success or yielded disappointing results. There has been a strong dependence on seismic data to interpret stratal ages and the regional depositional history because of the limited number of wells, which are all in the more proximal region. In October 2017, the International Ocean Discovery Program Expedition 369 drilled a hole at Site U1512 that straddled the Australian Geological Survey Organisation Survey s065 line 06 on the continental slope, ~67 km south-east of the Jerboa 1 well. The recovered core is the most extensive lithological dataset acquired from the basin and consists of a 10 m thick Pleistocene ooze overlying a 690 m succession of Turonian–Santonian strata. The Cretaceous strata consist of silty claystone with a few thin beds of glauconitic and sideritic sandstone (<32 cm thick). The Tiger Supersequence is substantially thicker than had been anticipated. Preliminary palynofacies analysis indicates a prevailing dysoxic marine environment, with the assemblage dominated by phytoclasts (40–90% of the assemblage). This may have been a consequence of high rates of freshwater runoff into the restricted basin. Rapid sedimentation rates (up to 260 m/Myr), the silt content (2–25%) and the palynofacies suggest the strata were deposited primarily by hyperpycnal and hypopycnal flows. These new datasets will provide a means to re-evaluate the palaeogeography of the basin and its resource potential.