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Bringelly Shale is a component of the Wianamatta shale of sedimentary rocks in the Sydney Basin of eastern Australia. Formed in the Middle Triassic Period, it has an extensive outcrop in the Western Sydney of Sydney and occupies around one third of the Sydney sheet.
Occupying much of the Cumberland Plain, the shale has its greatest geographical extent at Bringelly (its namesake), near the suburb of Liverpool. Featuring sandstone lentils, it is the topmost layer of the Wianamatta Group and the youngest Triassic sedimentary rock unit in the Sydney Basin.
It is similar to Ashfield Shale in that both have low porosities, though differing in having a greater amount of calcareous, graywacke-type, Lithic sandstone sandstone bands and lenses, carbonaceous claystone, siltstone, laminite, but would lack siderite
Unlike the Ashfield Shale, it features sandstone lithology and lenticles that fluctuate from to in thickness, in addition to having a disposition for the thicker lens bands that are concentrated at the top of the rock. The sandstones within the shale are filled in channels that were created by rivers, which wind across the marshy lowlands.
Lithology
The shale is the topmost layer of sedimentary rock laid down by a coastal alluvial river delta over the older Hawkesbury sandstone in the Triassic Period. Wianamatta shale Dictionary of Sydney It transitions from an inlet or coastal swamp sheet at the bottom in a marshy plain deposited on the delta, to a more alluvial plain sediment at the top of the unit. It roamed through the rivers of Sydney, and accumulated sand at numerous locations, which it then solidified into sandstone.
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Description
The average thickness is around , though a maximum thickness of was recorded at Razorback, near Campbelltown. It was deposited in a swampy alluvial plain with winding streams that formed sporadic beds of sandstone. The shale is dark when unweathered just like the Ashfield Shale, and is usually a typical olive-green colour when weathering. Alloyed coal bands and lenses and iron oxide concretions have been observed in the shale. The shale is quarried in many western suburbs of Sydney for brick and miscellaneous ceramic manufacture. (1980). 9780724012503, Geological Survey of NSW. ISBN 9780724012503
Distribution
The disjointed sandstone lenses become thicker and more conspicuous from Western Sydney Regional Park and to the south of it, whereby shaping the hilly landscape between Campbelltown and Picton. Namely found on Old Hume Highway, approaching Picton, the sandstone cliffs that become thicker are roughly around in height. The steep banks of the sandstone lentils influence the flora of the Cumberland Plain Woodland, with such escarpments being observed in Western Sydney Dry Rainforest areas. Wianamatta Group by Step Inc. Retrieved May 12, 2025. The shale runs into the Potts Hill Sandstone through a minor transitional zone of vacillating sandstone and shale bands.
See also
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