Abstract:

The Permian-Triassic (Gondwanan) basins and foldbelts along the Panthalassan margin of the Gondwanaland province of Pangea developed on a basement of Proterozoic and Paleozoic rocks in Antarctica and southern Africa and on a basement of foldbelts terminally deformed at the end of the Devonian (360 Ma) in southern South America and in the mid-Carboniferous (320 Ma) in eastern Australia. With the latest Carboniferous (290 Ma) onset of Pangean extension I, deposition resumed after a lacuna in Gondwanaland with glacigenic sediment. Together with post-Hercynian Europe on the other side of Pangea, postorogenic eastern Australia was subjected to continuing dextral transtension that produced an orocline, related pull-apart basins, and widespread volcanism. At the other end of the Panthalassan margin of Gondwanaland, a new magmatic arc and yoked foreland basin arose in southern South America at about 290 Ma, and by 275 Ma had propagated 4,000 km by migration of a junction of subduction parallel and normal to the margin to reach a point opposite Africa and the Ellsworth Mountains of Antarctica. This (Sakmarian) time saw an ephemeral postglacial marine transgression that flooded much of eastern and southern Australia, the south Atlantic margins of southern Africa and South America, and possibly the Transantarctic basin. The following regression was marked by widespread deposition of coal in all parts of the margin except southern South America. By 265 Ma, the magmatic arc and foreland basin had reached the Bowen Basin in northeastern Australia, and from 258 Ma to the 250 Ma end of the Permian, the foreland basin in Antarctica and Australia subsided rapidly beneath the load of the overthrusting magmatic orogen to accumulate a piedmont of thick tuffaceous coal measures. Both coal and tuff disappeared in Antarctica and Australia at the Permian- Triassic boundary (250 Ma) and were succeeded by barren measures with redbeds, all probably as a result of the global greenhouse warming generated by the eruption of the Siberian Traps. The magmatic arc continued its northward migration, and plutonic activity in eastern Australia continued unabated. The intermittent thrusting of the foldbelt and adjacent foreland basin during the Permian (Gondwanides I) was followed in the mid-Triassic (235-230 Ma) by terminal thrusting along the entire margin (Gondwanides II). Pangean extension II in the Carnian (230 Ma) generated basins in the foldbelt upland, notably in southern South America and eastern Australia, as well as in the sump between the craton and the orogenic upland. Deposition of coal (oil shale in southern South America) resumed after an Early and Middle Triassic gap of 20 million years. The Permian-Triassic (Gondwanan) sedimentary and foldbelt successions were capped in the Jurassic by a flood of silicic volcanics in southern South America and by an even bigger flood of tholeiitic basalt in southern Africa, Antarctica, and Tasmania, and scattered volcanics in southeastern Australia. East Antarctica was rifted from West Antarctica on one side, from Australia on another, and on yet another drifted from Africa by seafloor spreading.