The Mittagong Formation is a

sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

unit in the

Sydney Basin The Sydney Basin is an 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 eastern side now subsided beneath the Tasman Sea. ...

in eastern

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

Formation

Laid down in the

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

Period, it may be seen as an interval of interbedded fine-grained

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

and shale between the

Ashfield Shale Ashfield Shale is part of the Wianamatta group of sedimentary rocks in the Sydney Basin. It lies directly on contemporaneously eroded Hawkesbury sandstone or the Mittagong formation. These rock types were formed in the Triassic Period. It is nam ...

(above) and the

Hawkesbury sandstone Sydney sandstone is the common name for Sydney Basin Hawkesbury Sandstone, one variety of which is historically known as Yellowblock, and also as "yellow gold" a sedimentary rock named after the Hawkesbury River north of Sydney, where this ...

(below). The maximum thickness around Sydney may be ten metres. Near Town Hall railway station, the formation is 8 metres thick. In the type area at Mittagong it is 15 metres thick.

Whereabouts

In northern

Sydney Sydney ( ) is the capital city of the state of New South Wales, and the most populous city in both Australia and Oceania. Located on Australia's east coast, the metropolis surrounds Sydney Harbour and extends about towards the Blue Mountain ...

it can be seen in several areas, such as

West Pymble West Pymble is a suburb on the Upper North Shore of Sydney in the state of New South Wales, Australia north-west of the Sydney Central Business District in the local government area of Ku-ring-gai Council. Pymble is a separate suburb to the ea ...

and

Mount Ku-ring-gai Mount Kuring-gai is an outer suburb of Northern Sydney, in the state of New South Wales, Australia. Mount Kuring-gai is located 31 kilometres north-west of the Sydney central business district, in the local government area of Hornsby Shire. ...

. This rock formation is associated with the critically endangered

Sydney Turpentine-Ironbark Forest The Sydney Turpentine-Ironbark Forest (STIF) is dry sclerophyll forest community of Sydney, New South Wales, Australia, that is typically found in the Inner West and Northern region of Sydney. It is also among the three of these plant communitie ...

References

Geologic formations of Australia Triassic Australia Sandstone formations Shale formations Geology of New South Wales {{Australia-geology-stub

Formation

Whereabouts

See also

References