Microfossils from the section intersected in Cootanoorina 1 were analysed to enable correlation and age determination of the various rock units and interpretation of the Permian depositional environments. Age determinations include: Unit 3 (2925-3111 feet), Devonian; Units 2 and 1 (1695-2925 feet), Lower Permian; Mount Toondina Beds (615-1695 feet), Lower Permian; Algebuckina Sandstone (467-615 feet), no fossil evidence; Cadna-owie Formation (370-467 feet), Lower Cretaceous (Valanginian to Aptian); Bulldog Shale (0-370 feet), Lower Cretaceous (Valanginian to Aptian). The presence of foraminifera and organic-walled microplankton indicates marine influence during the deposition of Unit 1 in the Lower Permian. Below 2200 feet in Unit 2, the foraminiferal fauna is diverse though entirely arenaceous, and microplankton occur consistently. It is suggested that deposition occurred in a barred basin with rising temperatures and salinity. Anhydritic sediment above 2200 feet coincides with the sudden disappearance of foraminifera. Fossil evidence indicates that during deposition of the black shale facies above 1745 feet bottom conditions were stagnant and saline, with a surface layer of fresher water. The Mount Toondina Beds are a paludal, fluviatile and lacustrine complex; no marine fossils were found.