Arthur Mory

Lower Carboniferous strata are preserved only north of 24°S, but during the Middle Carboniferous to Permian the northern Perth and Southern Carnarvon Basins formed a single intracratonic depositional realm from 32°S to 23°S within the East Gondwana interior rift system. This succession is dominantly of shallow marine to fluvial origin, and is relatively undeformed (outcrop dips rarely exceed 15°) and has not been deeply buried due to a general lack of sedimentation on the eastern margin of the Perth Basin and across the
Southern Carnarvon Basin throughout the Triassic–Jurassic and Cenozoic. This guide describes the most informative Carboniferous–Permian outcrops in the basins in terms of stratigraphy, sedimentology and paleontology, but also includes Pleistocene–Holocene localities that have been used as models for carbonate deposition, of which the carbonate banks and stromatolites at Shark Bay are the most renowned.
Early Carboniferous deposition in a broad interior sag basin produced two major carbonate–sandstone sequences: the Tournaisian Moogooree Limestone to Williambury Sandstone cycle; and the possible Visean Yindagindy Formation to Harris Sandstone cycle. Carbonates in the basal formations of each cycle, although poorly dated, include microbialites, ooid–peloidal and skeletal grainstones–packstones, indicating warm and occasionally hypersaline conditions.
Mid-Carboniferous–Permian deposition in a narrow interior rift, over 1000 km long, was dominated by alternating marine and terrestrial facies with marine conditions increasing to the north. A 5-km thick shallow-marine succession formed in the Merlinleigh Sub-basin in the north, and a somewhat thinner succession, including coal measures, accumulated to the south in the Perth Basin. Carboniferous to early Sakmarian glacially-influenced sediment rapidly infilled the initial basin that had an irregular topography (probably shaped by thick continental ice sheets, and affected by a later phase of the Alice Springs Orogeny). By the mid-Sakmarian, a shallow sea floor with a very low gradient developed throughout the region: water depths probably did not exceed 50 m during the Early–Middle Permian. Subsidence apparently just exceeded sediment influx, and variations in these parameters resulted in distinct depositional cyclicity of several orders. In the post-glacial successions, two major depositional cycles of late Sakmarian to
mid-Artinskian and late Artinskian to at least Roadian indicate warming sea conditions during the Sakmarian, with a minor cooling phase during the middle or late Artinskian.

Throughout most of the Early Carboniferous shelf sedimentation extended across the Tamworth Belt for a present distance of 35 km to near the eastern margin of the Belt. These sediments are dominated by muds and silts, with minor near shore sands, deposited by traction currents, along the western margin of the Belt. Much of the coarser sediment is inferred to have bypassed the shelf via channels, now comglomerate‐filled, to be deposited in base‐of‐slope environments east of the Tamworth Belt. The Texas and Sandon beds possibly represent these base‐of‐slope deposits. The New England Arch has not affected sedimentation in the Tamwortb Belt until post‐Visean (Late Carboniferous) times.

Inter-basinal correlations for the Cambrian to Carboniferous successions of Western Australia are mostly poorly constrained, largely due to unfavourable biogeographic factors, but also because biostratigraphic studies have been skewed to certain basins and intervals. By comparison, Permian inter-basinal correlations have benefited from numerous, mostly unpublished, spore-pollen studies, but correlations to the international timescale are poorly constrained because calibration of the latter is based largely on marine species that are rare in Australia. Nevertheless, a moderately robust correlation is possible for intervals of 10–30 m.y. in the Paleozoic, and reveals broad similarities between basins implying overriding far-field tectonic influences across west Australia. Devonian–Carboniferous events in central Australia—grouped together as the Alice Springs Orogeny—have the most obvious control, at least on the northern basins, but the underlying mechanisms, especially for the initi...