Amadeus Basin

The Amadeus Basin is graced with spectacular outcrops of Cambrian rocks, and its sequences (see figure 6.5) should be pivotal in resolving correlation problems between the South Australian basins and the Georgina Basin, since the archaeocyath-bearing Lower Cambrian rocks allow correlation with the former, and the trilobite-bearing Middle Cambrian permits correlation with the latter. Unfortunately, Lower and Middle Cambrian biostratigraphy of the Amadeus Basin is basically undeveloped, and sequence stratigraphy results largely from seismic stratigraphy, down-hole geophysics, and sedimentation patterns.

Of its four sedimentary compartments, only the easternmost Ooraminna Sub-basin can be correlated with reasonable confidence into the Georgina Basin. This depo-center contains the four diagnostic trilobite genera that define the Ordian stage (sensu stricto) in the lower "Giles Creek Dolomite" (see figure 6.5), which we regard as the carbonate lateral equivalent of the evaporitic Chandler Formation. This last formation,

Figure 6.6 Sequence stratigraphie relationship of formations in the Georgina Basin (after Southgate and Shergold 1991).

comprising 95 percent halite, represents the time of maximum desiccation in central Australia. Minor evaporites recorded in the Moodlatana Formation of the Arrowie Basin, and those of the Gum Ridge Formation and Thorntonia Limestone of the Georgina Basin may be correlated through this Ordian event. The Amadeus Basin regrettably offers no assistance in the resolution of the Early-Middle Cambrian epoch boundary.

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