Evolution of the outer basin high, Ceduna Sub-basin, southern Australia

Recent exploration in the Bight Basin has identified an uplifted area on the outer margin of the Ceduna Shelf, known as the outer basin high. The Tiger Supersequence, a potential source rock, thins onto the uplifted area, so the timing and extent of uplift has implications for petroleum system maturity. The outer basin high is 15–40 km wide and extends along the south-western flank of the Ceduna Sub-basin, beneath the outer flank of the Ceduna Terrace. Relative uplift of greater than 2000 m occurs within the area. The outer basin underlies a transitional zone of deformation between the extensional faulting and outer fold and thrust regions of the overlying White Pointer and Hammerhead delta systems. Detailed mapping using the recently released Ceduna 3D seismic dataset reveals two main episodes of relative uplift, in the Santonian and again in the Maastrichtian to Eocene. The first phase of relative uplift is associated with thinning of the Tiger Supersequence onto the high. The second phase is identified as a decrease in thickness of the Hammerhead Supersequence overlying the high. The exact timing of this uplift is difficult to constrain due to truncation of the Hammerhead Supersequence by the basin-wide Eocene unconformity, however, estimates of the amount of uplift are based on seismic mapping.