Bulgo Sandstone 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 particle ...

occurring 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. This stratum is up to 100 metres thick, formed in the early

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 ...

. A component of the

Narrabeen Group The Narrabeen group of sedimentary rocks occurs in the Sydney Basin in eastern Australia. This series of rocks was formed in the Triassic Period. Geology It includes various rock types including lithic sandstone, quartz sandstone, siltstones, ...

of sedimentary rocks. It consists of layers of fine to medium-grained quartz- lithic

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 ...

, with lenticular

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especia ...

interbeds. Often seen as a grey-green colour when exposed, the Bulgo sandstone contains a high level of particles of volcanic rocks, and is dissimilar to other Sydney sandstones, such as

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 ...

and

Newport Formation The Newport Formation is a geologic formation outcropping in the Sydney Basin in eastern Australia. This stratum is up to 49 metres thick. Formed in the mid- Triassic, it is part of the Narrabeen Group of sedimentary rocks. See also * Sydn ...

. The rock breaks down to create a relatively fertile clayey soil. These soils contribute to the

rainforest Rainforests are characterized by a closed and continuous tree canopy, moisture-dependent vegetation, the presence of epiphytes and lianas and the absence of wildfire. Rainforest can be classified as tropical rainforest or temperate rainfo ...

growth in the northern

Illawarra The Illawarra is a coastal region in the Australian state of New South Wales, nestled between the mountains and the sea. It is situated immediately south of Sydney and north of the South Coast region. It encompasses the two cities of Wollongo ...

. Bulgo sandstone may be seen at the "figure eight" rock pool at

Royal National Park The Royal National Park is a protected national park that is located in Sutherland Shire in the Australian state of New South Wales, just south of Sydney. The national park is about south of the Sydney central business district near the l ...

and at Long Reef in the northern Beaches in Sydney. A fossil of the giant

salamander Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All ten ...

(Bulgosuchus gargantua) was found at Long Reef.

References

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