Perth Basin: Stratigraphy
Related Resources : Perth Basin
Letters in brackets after the formation name represent shorthand symbols used on geological maps.
Quaternary And Recent
The Quaternary and Recent sedimentation of the Perth Basin is represented by thin, impermanent sand dune systems, biogenic limestones, sandstones and some shales deposited during the last ~20 million years and during ice ages.
Upper Cretaceous glauconitic marl, infrequently developed on top of the Coolyena Group.
- Coolyena Group - Upper Cretaceous marine sediments.
Poison Hill Greensand Kcp consists of pale yellow unconsolidated weathered clay, glauconitic sandstone and shale. It conformably overlies the Gingin Chalk and is in turn overlain by unconsolidate Quaternary sands and alluvium.
Gingin Chalk Kcg is a weakly consolidated fossiliferous chalk composed of coccoliths, which interfingers and conformably overlies the Molecap Greensand.
Molecap Greensand Kcm is a fine to medium grained marine glauconite sandstone which uncconformably overlies the Osborne Formation.
- Osborne Formation Kco conformably overlies the Triassic Leederville Formation, and is composed of a marine sandstone, shale and interbedded 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.
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.
- Lesueur Sandstone Formation Trl
- Woodada Formation Trw
- Kockatea Shale Trk
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