Reassessment of the geology and exploration potential of the Western Australian Amadeus Basin

in central Australia. The majority lies in the Northern Territory, but about 30 000 km 2 is exposed in eastern Western Australia, with more beneath the Canning Basin to the west. The basin contains a thick Neoproterozoic to Paleozoic succession, although confirmed Paleozoic strata are limited in WA, and underwent regional folding during the Petermann (Ediacaran–Cambrian) and Alice Springs (mid Paleozoic) Orogenies. The NT portion is well known and moderately explored, but remoteness, difficult access, and poor exposure have conspired to see very little activity in the western Amadeus Basin since first-pass reconnaissance mapping by the Bureau of Mineral Resources in the early 1960s (Wells et al., 1961, 1964). Apart from the Heavitree Quartzite and its correlative the Dean Quartzite, and the overlying Bitter Springs Formation, separate stratigraphic schemes were devised for eastern and western portions of the basin (Wells et al., 1970). Recent fieldwork by the Geological Survey of Western Australia indicates that the western Amadeus Basin shows much closer similarity to the well-established stratigraphy within the NT than previously reported and reveals new insights into the geological history of the area, necessitating a revision of basin-wide correlations (Fig. 1). Ultimately, the western Amadeus Basin should provide an important link between the Officer and eastern Amadeus Basins. The key has been understanding the stratigraphic complexity of the poorly exposed Boord Formation and its relationship to the Carnegie Formation. These units disconformably overlie the Bitter Springs Formation in the north and south of the area, respectively, and were regarded as lateral equivalents. The Boord Formation includes glacigene strata and was previously correlated with either the Areyonga Formation (Wells et al., 1970; Weste, 1989) or Olympic Formation/Pioneer Sandstone (Grey, 1990), the glacigene units of the eastern Amadeus succession, and correlatives of the Sturt or Elatina glaciations of the Adelaide Rift Complex, respectively. Our fieldwork indicates that the Boord Formation contains not one, but two glacial units, several disconformities, and significant pre- and post-glacial intervals. In total it contains likely correlatives of the ‘Finke beds’ (an informal unit recognized in several petroleum wells in the NT: Grey et al., in press) and Areyonga, Aralka, Olympic, Pertatataka, and Julie Formations of the northeastern Amadeus Basin. We propose eventual abandonment of the ‘Boord Formation’ as presently defined, but until a new stratigraphy is finalized we use this name informally for the composite package. The new correlations are based on lithostratigraphy with strong support from stromatolite biostratigraphy. Unique stromatolite assemblages can be used to subdivide the Bitter Springs Formation into Gillen and Loves Creek Members, as in the NT, and to link the inferred correlatives of the ‘Finke beds’, upper Aralka, and Julie Formations to their counterparts in the eastern Amadeus and other basins throughout Australia. The Carnegie Formation is a thick, immature siliciclastic unit, strongly resembling the lower part of the Ediacaran– Cambrian Arumbera Sandstone in the NT. Both formations contain Arumberia, a problematic biogenic structure first described from the Arumbera Sandstone (Glaessner and Walter, 1975). Although there is minor interfingering at the Boord–Carnegie Formation contact, we consider the latter to be mostly younger than the ‘Boord Formation’. In the south, the Carnegie Formation overlies the Bitter Springs Formation with an angular unconformity, the intervening succession having been presumably uplifted and eroded in that area. Together, the Carnegie Formation and overlying Sir Frederick Conglomerate, Ellis Sandstone, and Maurice Formation are interpreted as a synorogenic package related to