Bringelly Shale is a component of the Wianamatta group of

sedimentary Sedimentary rocks are types of rock formed by the cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or deposited at Earth's surface. Sedime ...

rocks in the

Sydney Basin The Sydney Basin is an Interim Biogeographic Regionalisation for Australia, interim Australian bioregion and is both a structural entity and a depositional area, now preserved on the east coast of New South Wales, Australia and with some of its ...

of eastern

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

. Formed in the

Middle Triassic In the geologic timescale, the Middle Triassic is the second of three epoch (geology), epochs of the Triassic period (geology), period or the middle of three series (stratigraphy), series in which the Triassic system (stratigraphy), system is di ...

Period, it has an extensive outcrop in the western parts of

Sydney Sydney is the capital city of the States and territories of Australia, state of New South Wales and the List of cities in Australia by population, most populous city in Australia. Located on Australia's east coast, the metropolis surrounds Syd ...

and occupies around one third of the Sydney sheet. Occupying much of the Cumberland Plain, the

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of Clay mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...

has its greatest geographical extent at Bringelly (its namesake), near the suburb of

Liverpool Liverpool is a port City status in the United Kingdom, city and metropolitan borough in Merseyside, England. It is situated on the eastern side of the River Mersey, Mersey Estuary, near the Irish Sea, north-west of London. With a population ...

. Featuring

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

lentils The lentil (''Vicia lens'' or ''Lens culinaris'') is an annual plant, annual legume grown for its Lens (geometry), lens-shaped edible seeds or ''pulses'', also called ''lentils''. It is about tall, and the seeds grow in Legume, pods, usually w ...

, it is the topmost layer of the Wianamatta Group and the youngest Triassic

sedimentary rock Sedimentary rocks are types of rock (geology), rock formed by the cementation (geology), cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or de ...

unit in the

Lithology

The shale is the topmost layer of

laid down by a coastal alluvial

river delta A river delta is a landform, archetypically triangular, created by the deposition of the sediments that are carried by the waters of a river, where the river merges with a body of slow-moving water or with a body of stagnant water. The creat ...

over the older

Hawkesbury sandstone Sydney sandstone, also known as the Hawkesbury sandstone, yellowblock, and yellow gold, is a sedimentary rock named after Sydney, and the Hawkesbury River north of Sydney, where this sandstone is particularly common. It forms the bedrock f ...

in the

Triassic Period The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is the ...

. It transitions from an

inlet An inlet is a typically long and narrow indentation of a shoreline such as a small arm, cove, bay, sound, fjord, lagoon or marsh, that leads to an enclosed larger body of water such as a lake, estuary, gulf or marginal sea. Overview In ...

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. It is similar to Ashfield Shale in that both have low porosities, though differing in having a greater amount of

calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime (mineral), lime or being chalky. The term is used in a wide variety of Science, scientific disciplines. In zoology ''Calcare ...

, graywacke-type, lithic

bands and lenses, carbonaceous

claystone Mudrocks are a class of fine-grained siliciclastic sedimentary rocks. The varying types of mudrocks include siltstone, claystone, mudstone and shale. Most of the particles of which the stone is composed are less than and are too small to ...

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility. Although its permeabil ...

, laminite, but would lack sideritic

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...

bands that Ashfield Shale has. Featuring lumpy clay minerals, it swells and decays rapidly on submergence in water and is generally less durable.

Description

The average thickness is around , though a maximum thickness of was recorded at

Razorback A feral pig is a pig, domestic pig which has gone feral, meaning it lives in the wild. The term feral pig has also been applied to wild boars, which can interbreed with domestic pigs. They are found mostly in the Americas and Australia. Razorb ...

, near Campbelltown. It was deposited in a swampy

alluvial Alluvium (, ) is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. Alluvium is also sometimes called alluvial deposit. Alluvium is ...

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 weathered. Alloyed

coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other Chemical element, elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal i ...

bands and lenses and

iron oxide An iron oxide is a chemical compound composed of iron and oxygen. Several iron oxides are recognized. Often they are non-stoichiometric. Ferric oxyhydroxides are a related class of compounds, perhaps the best known of which is rust. Iron ...

concretions have been observed in the shale. The shale is quarried in many western suburbs of Sydney for brick and miscellaneous

ceramic A ceramic is any of the various hard, brittle, heat-resistant, and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcela ...

manufacture. Unlike the Ashfield Shale, it features sandstone

lithology The lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples, or with low magnification microscopy. Physical characteristics include colour, texture, grain size, and composition. Lit ...

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

sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

s in channels that were created by rivers, which wind across the marshy lowlands.

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.

References

{{Reflist Geology of New South Wales Geologic formations of Australia Triassic Australia Shale formations Sandstone formations

Lithology

Description

Distribution

See also

References