shale-sandstone sequence from base upwards. Warnbro Group - Early Cretaceous marine sediments representing a transgression. Parmelia Formation (J-Kp) forms the topmost hydraulic unit of the Yarragadee Aquifer. It is composed of 100–200 m thickness of well sorted fluvial sandstone deposited in the latest Jurassic to early Cretaceous. It includes a basal siltstone of lagoonal to lacustrine environment, the Otowiri Siltstone, which acts as an aquitard. Leederville Formation (Kll) sandstone, siltstone, shale and mudstone deposited in deeper marine environments, with finer sediments predominant in the upper part of the unit. The unit attains a maximum thickness in the axis of the Yanchep Syncline is ~700 m, and thins eastward to approximately 500 m. The Leederville Formation interfingers and merges with the underlying Parmelia Formation in the north of the Perth Basin. Gage Formation (Kwg) is a shallow lagoonal sandstone and shale deposited in shallow marine beach-dune-lagoonal environments. Jurassic Yarragadee Formation (Jy) is one of the thickest units in the Perth Basin and forms a significant freshwater aquifer. It is composed primarily of non-marine fluviatile feldspathic, poorly sorted sandstones which are porous and poorly cemented, hence allowing for considerable groundwater reserves. The Yarragadee Formation grades from a shale-siltstone dominated base to a cleaner sandstone in the upper portions of the formation, probably representing increased subsidence or filling of the basin during the late Jurassic. Cadda Formation (Jd) conformably underlies the Yarragadee Formation and is composed primarily of shale and siltstone, with occasional beds of very coarse sandstone. The upper portions of the unit are composed of a marl grading into a marine limestone, representing stable tectonics at this time. Cattamarra Coal Measures (Jc) are a sequence of non-marine, probably fluviatile sandstones, shales and silts including bituminous coal, and are up to 300 m thick. The Cattamarra Coal Measures conformably overly the Eneabba Formation. Eneabba Formation (Je) is a lower-Jurassic terrigenous red-bed unit composed of interbedded sandstone with variably coloured limestone. The Eneabba Formation is conformable with the Lesueur Sandstone in the south of the Perth Basin and unconformable with the Kockatea Formation in the north, suggesting it is transgressive. Triassic Kockatea Shale (Trk) Lesueur Sandstone (Trl) Woodada Formation (Trw) Economic geology Cenozoic sand dune systems are locally being mined for mineral sands, mainly rutile (a source of titanium ) and zircon, by Iluka Resources and other companies. Various formations from Cenozoic to Jurassic age are economically significant freshwater aquifers. Younger aquifers are