Oceanic crust to the east was created by the seafloor spreading that formed the Tasman Sea in the Late Cretaceous and Paleogene. The crust to the south and west was formed during the Cenozoic, and perhaps the latest Cretaceous, by the seafloor spreading that led to the separation of Australia and Antarctica. Sampling cruises have shown that the slope is underlain by continental basement and that Upper Cretaceous and Paleogene shallow-marine sandstone, siltstone, and mudstone are widespread in deep water west of Tasmania, overlain by Oligocene to Holocene pelagic carbonates. The overlying sequences in faulted basins include known Oligocene to Holocene pelagic carbonates and Paleogene marine mudstones, and seismic evidence suggests they also contain Cretaceous sediments. The top of the rise is a gentle dome with low slopes, but slopes are generally steeper between 2000 and 4000 m.
Slopes are generally low, but considerably greater on the plateau's flanks.
Atop the plateau is the Cascade Seamount guyot, which formed as the result of hot spot volcanism and has yielded Eocene and younger shallow-water sandstone and volcanics. These are underlain by continental basement rocks. The structural setting of Sites 1168-1172 is shown in Figure 9 . They were generated by the northwest movement of Australia away from Antarctica. The three sets of faults all have throws reaching as much as 3 km.