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. The continental slope west of Tasmania falls fairly regularly from 200 to 4000 m. Sampling cruises have shown that the slope is underlain by continental basement and that Late Cretaceous and Paleogene shallow-marine sandstone, siltstone, and mudstone are widespread in deep water west of Tasmania, overlain by Neogene pelagic carbonates. The overlying sequences in faulted basins include known Neogene 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. Site 282 was drilled on a basement high west of Tasmania. This sequence includes much of the Cenozoic but contains four major unconformities. The sediments rest on a basalt flow of presumed Tertiary age.