Outline of Phanerozoic History of Australia and Surrounding Oceanic Region: ABSTRACT

Abstract

The Tasman orogenic zone has been accreted onto the eastern side of a Precambrian shield. A series of transitional to postorogenic basins has been superimposed. The Tasman orogenic zone, which was mobile from the Cambrian to Early Cretaceous, underwent progressive but stepwise cratonization with culminations or orogenesis in the Early Ordovician, Middle Devonian, Early Permian, and Early Cretaceous. Relicts of this orogenic zone crop out in New Zealand and New Caledonia, and are inferred in the foundered continental blocks of the Queensland Plateau, Lord Howe Rise, Norfolk Ridge, and the Campbell Plateau. The Tasman orogenic zone, which differs considerably from the classic model, can be explained as an active plate boundary between a Paleopacific-oceanic plate and a continental plate. Mountain building has been of a modest scale and no great crustal thicknesses have been developed. The sediment filling the various basins is mainly clastic and, in the early and middle Paleozoic at least, had a dominant southerly source. Antarctica must have been a significant contributor, and probably remained so even in the Permian and early Mesozoic when parts of the Eastern Highlands were elevated. In the early Paleozoic, carbonate rocks are more abundant in the north of the continent. Fragmentation of this part of Gondwanaland commenced in the west in the Late Jurassic to Early Cretaceous with the formation of the Wharton basin. In the east, the Tasman Sea started to form in the Late Cretaceous. Although an incipient rift formed across southern Australia in the middle Mesozoic, new seafloor formation and northward motion of Australia away from Antarctica did not commence until the Paleocene. Eastward accretion of oceanic crust took place in the Eocene and Oligocene (the Coral Sea and the South Fiji basin). Some phases of plate convergence occurred in this time interval resulting in overthrusts of oceanic crust. Relocation of the Pacific plate boundary inside the Melanesian arcs resulted in some of the sea floor, formed during extension, being consumed from the Mioc ne onward. Folding and uplift in the island of New Guinea also took place in the later Tertiary and Quaternary. The continental shelf and thick sediment accumulations in marginal basins have formed as a response to rifting. End_of_Article - Last_Page 1453------------