Fig. 5: Schematic of Australo-Antarctic margin evolution.

a, Before Gondwana break-up (pre-160 Ma), transcontinental fluvial drainage systems flowed from the highlands of interior East Antarctica to the northwestern coast of Australia⁴³. b, Following continental break-up and seafloor spreading onset at ~80 Ma, a small (~200 m) escarpment formed along parts of the southern Australian margin, and an interior drainage network was established on the inland side. In East Antarctica, rivers eroded down to the new base level, forming a low-lying, seaward-dipping coastal plain. c, After ~34 Ma, Australia’s climate became increasingly arid, and the interior drainage network became extinct. A limestone seabed became subaerially exposed during the Miocene, forming the Nullarbor Plain⁵⁹. Following ice-sheet growth, remnants of the East Antarctic fluvial planation surface were surficially scoured by ice, but the first-order inherited fluvial structure was preserved due to prevailing low subglacial erosion rates in these areas. Contemporaneously, fast-flowing, warm-based ice selectively exploited existing structural weaknesses (red dashed lines) and/or river valleys to erode deep glacial troughs between the flat-surface fragments.