And one of the largest countries on Earth, lying between the

The Mesozoic and Cenozoic eras

The coal measures of the Permian gave way to barren red beds in the early part of the Triassic Period (about 252 to 247 million years ago). By 230 million years ago the foreland basin of eastern Australia had been overthrusted by the mountain belt, and a second epoch of black-coal formation opened in eastern Australia (southeastern Queensland and Tasmania) and in South Australia (Leigh Creek). Another foreland basin became established behind the magmatic arc along the eastern margin, and a set of basins, including the Great Artesian Basin, subsided over the east-central part of Australia. Thick sand was deposited over the area of rifting that became the western and northwestern margins of Australia as Gondwanaland was breaking up and seafloor spreading was beginning in the northwest during the Late Jurassic (about 164 to 145 million years ago) and in the west during the Early Cretaceous (about 145 to 100 million years ago). Subsequent burial of the sand by sediment of late Mesozoic and Cenozoic age (about 66 million years old or younger) generated the giant natural gas field at Rankin on the North West Shelf. Rifting between Australia and Antarctica started in the Late Jurassic and culminated with the separation of the continents and the beginning of (very slow) seafloor spreading in the Late Cretaceous (about 100 to 66 million years ago). The other momentous event at that time took place in eastern Australia. The shallow sea that had covered nearly half of Australia during the Early Cretaceous retreated when the long-enduring Chilean-type subduction off eastern Australia was replaced by Mariana-type subduction and back-arc spreading in the Southwest Pacific Ocean that carried New Zealand and the submarine Lord Howe Rise away from Australia.