Narrabeen Shale
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The Narrabeen group of
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 ...
s occurs in the Sydney Basin in eastern Australia. This series of rocks was formed in the
Triassic The Triassic ( ) is a geologic period and system (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Year#Abbreviations yr and ya, Mya), to the beginning of the Jurassic Period 201.36 ...
Period.


Geology

It includes various rock types including 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 ...
,
quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...
sandstone, siltstones, claystones, conglomerate and
shales 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, especiall ...
, some of which have
fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
s of plants and fish. Partly in these rocks plants, fish and amphibious animals are petrified. The red and green shales of the Narrabeen Group are water-tight over the sandstone bodies and the shale of Bald Hill, which forms the top layer of the Narrabeen Group, forms a regional water-barrier layer. Over the Narrabeen Group, the younger
stratigraphic Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithostra ...
formation of Hawkesbury sandstones accumulated.


Structure

Above the Narrabeen group is the younger less fertile
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 are
Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last ...
sedimentary rocks including measures of
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 elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when ...
broadly known as the Illawarra Coal Measures.


Whereabouts

The Narrabeen group is most famously seen as The Three Sisters in the Blue Mountains. It can also be seen in various places in the Sydney Basin, such as Long Reef near
Narrabeen Narrabeen is a beachside suburb in northern Sydney, in the state of New South Wales, Australia. Narrabeen is 23 kilometres north-east of the Sydney central business district, in the local government area of Northern Beaches Council and is ...
, and at sea level around Broken Bay.


See also

* Sydney Basin *
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 ...
*
Banks Wall Sandstone Banks Wall Sandstone is a type of sedimentary rock occurring in the Sydney Basin in eastern Australia. This stratum is up to 115 metres thick. Often seen in the Blue Mountains, such as at the Three Sisters at Katoomba. The rock is mostly q ...
*
Burra-Moko Head Sandstone Burra-Moko Head Sandstone is a type of sedimentary rock occurring in the Sydney Basin in eastern Australia. This stratum is up to 112 metres thick. The rock is composed of quartzose to quartz lithic sandstone. It is situated below the Mount Y ...
*
Mount York Claystone Mount York Claystone is a narrow band of sedimentary rocks occurring in the Sydney Basin in eastern Australia. This stratum is up to 13 metres thick. Mount York Claystone consists of red brown claystones, of fineā€grained and coarsely ooliti ...
*
Munmorah Conglomerate Munmorah Conglomerate is a geologic formation in the Sydney Basin in eastern Australia. This stratum is up to 140 metres thick. Formed in the early-Triassic, it is part of the Narrabeen Group of sedimentary rocks. This formation includes medium t ...
*
Terrigal Formation The Terrigal Formation is a geologic formation in the Sydney Basin in eastern Australia. Commonly seen in the Central Coast region, this stratum is up to 330 metres thick. Formed in the early to mid Triassic, it is part of the Narrabeen Group of ...
*
Newport Formation (NSW) 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 ...
*
Garie Formation The Garie Formation is a narrow band of sedimentary rocks occurring in the Sydney Basin in eastern Australia. This stratum is up to 8 metres thick, situated below the sandstones of the Newport Formation. Formed in the mid-Triassic, it is part of ...
*
Bulgo Sandstone Bulgo Sandstone is a sedimentary rock occurring in the Sydney Basin in eastern Australia. This stratum is up to 100 metres thick, formed in the early Triassic. A component of the Narrabeen Group of sedimentary rocks. It consists of layers of fine ...
*
Bald Hill Claystone Bald Hill Claystone is a sedimentary rock found in the Sydney Basin in eastern Australia. It is part of the Clifton sub-group of the Narrabeen Group of sedimentary rocks. It was formed by weathering of the Gerringong Volcanics in the early Triass ...
*
Geology of New South Wales Geologically the Australian state of New South Wales consists of seven main regions: Lachlan Fold Belt, the Hunter-Bowen Orogeny or New England Orogen (NEO), the Delamerian Orogeny, the Clarence Moreton Basin, the Great Artesian Basin, the Sydne ...
*
Geography of Sydney The geography of Sydney is characterised by its coastal location on a basin bordered by the Pacific Ocean to the east, the Blue Mountains to the west, the Hawkesbury River to the north and the Woronora Plateau to the south. Sydney lies on a s ...


References

* http://australianmuseum.net.au/The-Sydney-Basin * https://web.archive.org/web/20090916073705/http://www.vnc.qld.edu.au/enviro/bluemtns/blue-b.htm Geologic groups of Oceania Geologic formations of Australia Triassic Australia Geology of New South Wales {{Geology-stub