• The Gogo Formation, identified by Wade (1936) and named by Guppy et al. (1958), represents the oldest inter-reef deposits in the southern region of the Lennard Shelf in the Canning Basin in the north of Western Australia. The Canning Basin reef began its growth in mid-Givetian times (based on miospores; see Grey 1992) and continued until the end of the Famennian. The flat-lying outcrops of the Gogo Formation occur over a large area (∼200 km2) between prominent outcrops of the Devonian reef complex to the east of Fitzroy Crossing, on Gogo and Mt Pierre Stations. They were first mapped by Teichert (1949) and then in more detail by Playford & Lowry (1966). The Gogo Formation is ∼700 m thick as measured from drill core and is the basinal lateral-facies equivalent of the Sadler Limestone Formation (marginal-slope facies), Pillara Limestone (platform facies), and Windjana Limestone (reef facies; see Playford et al. 2009) (Figure 1). In contrast to the subsurface thickness, the type-section thickness is ∼425 m (Guppy et al. 1958). Exposures of the Gogo Formation are poor, comprising dark fine-grained shales and siltstone with thin limestone interbeds containing randomly disposed calcareous concretions varying in size from a few centimeters to almost half a meter width. The formation of the concretions is thought to be bacterially mediated in anoxic muds and is sometimes associated with a buildup of sulfide (Playford & Wallace 2001).

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