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

The Paleozoic Era

Phanerozoic Australia is divided at the Tasman Line into two parts. Those are a western terrane of exposed Precambrian blocks and fold belts overlain by thin Phanerozoic basins and an eastern terrane of exposed Phanerozoic fold belts and basins.

Principal regimes

During Phanerozoic times, Australia has been marked by three regimes: Uluru (541 to 320 million years ago), Innamincka (320 to 97 million years ago), and Potoroo (the past 97 million years). Each regime, a complex of uniform plate-tectonic and paleoclimatic events at a similar or slowly changing latitude, generated a depositional sequence of distinct facies separated by gaps in deposition.



Cobar, New South Wales, Australia

Mine in Cobar, New South Wales, Australia.

Axel Strauss

The Paleozoic Era (about 541 to 252 million years ago) opened in Australia with the breakup of the Precambrian continent along the Tasman Line and the initial generation of the floor of the Paleo Pacific Ocean by seafloor spreading. In the Adelaide area, wedges of deepwater quartzose sediment advanced over the newly formed seafloor. On the northwestern side of Australia, widespread basalt erupted over the Precambrian platform, possibly during the initial generation of the Paleo Tethyan Sea, and was succeeded by deposition of shallow marine limestone with abundant fossil trilobites and archeocyathids. The initial Paleo Pacific marginal seafloor was subducted—i.e., forced under the edge of a converging plate into the hot mantle—at the end of the Cambrian Period (485 million years ago); concomitant deformation and granitic intrusion of the overlying deepwater sediments and those of the adjacent Adelaidean region formed the Delamerian fold belt. A similar cycle of marginal sea generation and subsequent Mariana-type subduction (within oceanic lithosphere) accreted a second fold belt to eastern Australia during the Ordovician Period (about 485 to 444 million years ago). That was followed by an interval of block faulting and widespread granitic intrusion in eastern Australia that produced a landscape similar to the present Basin and Range Province of the western United States; by the late Devonian Period (about 385 million years ago) the first of a series of magmatic orogenic arcs had become established by Chilean-type subduction (of oceanic lithosphere beneath continental lithosphere) on the eastern margin, and a thick succession of mainly sandstone and shale accumulated in the moatlike foreland basin between the mountain belt and the craton—the flat and relatively stable interior portion of the continent. At the same time, local uplifts in central Australia shed gravels into the Amadeus Basin. By the mid-Carboniferous Period (320 million years ago), central Australia was deformed by folding and thrusting along east-west axes, and eastern Australia was deformed by folding along north-south axes and a subsequent granitoid intrusion that consolidated the Lachlan and Thomson fold belts in an epoch of deformation that concluded the Uluru regime.

Australia had moved to higher latitudes so that the alpine uplands that followed the deformation were covered by the nucleus of a continental ice sheet. Only the highest peaks stood prominently above the surface of the ice in the form of nunataks, and the little sediment available was carried off the continent in ice streams. The melting of the ice sheet early in the Permian Period (i.e., about 290 million years ago) released the sediment into the newly subsiding basins of the Innamincka regime. Much of interior Australia was covered by broad basins. The eastern margin between the New England Fold Belt and the craton became a second foreland basin in which the rich seams of black coal in the Bowen Basin of Queensland and the Sydney Basin of New South Wales were deposited during the final 10 million years of the Paleozoic Era. Other economic resources in Paleozoic rocks are the reef gold in Victoria that triggered the first mining boom, lead and zinc at Cobar and Woodlawn in New South Wales, and natural gas in Permian sandstone in the Cooper Basin of South Australia.