Aust Cliff () is a 5.3

hectare The hectare (; SI symbol: ha) is a non-SI metric unit of area equal to a square with 100-metre sides (1 hm2), or 10,000 m2, and is primarily used in the measurement of land. There are 100 hectares in one square kilometre. An acre is a ...

geological Site of Special Scientific Interest A Site of Special Scientific Interest (SSSI) in Great Britain or an Area of Special Scientific Interest (ASSI) in the Isle of Man and Northern Ireland is a conservation designation denoting a protected area in the United Kingdom and Isle o ...

adjacent to the

Severn Estuary The Severn Estuary ( cy, Aber Hafren) is the estuary of the River Severn, flowing into the Bristol Channel between South West England and South Wales. Its high tidal range, approximately , means that it has been at the centre of discussions in t ...

, near the village of

Aust Aust is a small village in South Gloucestershire, England, about north of Bristol and about south west of Gloucester. It is located on the eastern side of the Severn estuary, close to the eastern end of the Severn Bridge which carries the M48 ...

South Gloucestershire South Gloucestershire is a unitary authority area in the ceremonial county of Gloucestershire, South West England. Towns in the area include Yate, Chipping Sodbury, Thornbury, Filton, Patchway and Bradley Stoke, the latter three forming part ...

, notified in 1954. The

Severn Bridge The Severn Bridge ( cy, Pont Hafren) is a motorway suspension bridge that spans the River Severn between South Gloucestershire in England and Monmouthshire in South East Wales. It is the original Severn road crossing between England and Wale ...

crosses the cliff. Its SSSI designation is due to the presence of

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 ...

beds. The site is famous for its

Rhaetic Rhaetic or Raetic (), also known as Rhaetian, was a language spoken in the ancient region of Rhaetia in the eastern Alps in pre-Roman and Roman times. It is documented by around 280 texts dated from the 5th up until the 1st century BC, which wer ...

bone bed A bone bed is any geological stratum or deposit that contains bones of whatever kind. Inevitably, such deposits are sedimentary in nature. Not a formal term, it tends to be used more to describe especially dense collections such as Lagerstätte. ...

, and is also the most productive locality in Britain for

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 ...

insects. The lower part of the cliff is a red

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 (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...

, with bands of nodules of pinkish-white

alabaster Alabaster is a mineral or rock that is soft, often used for carving, and is processed for plaster powder. Archaeologists and the stone processing industry use the word differently from geologists. The former use it in a wider sense that includes ...

. Above the red mudstone is green mudstone, followed by the Rhaetic bone bed at the base of a band of

black 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 ...

. Above the shale are cream-coloured

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

beds.The story of landscape and geology in South Gloucestershire
p.16

Paleofauna

References

External links

English Nature citation sheet for the SSSI
(accessed 9 July 2006) Sites of Special Scientific Interest in Avon Sites of Special Scientific Interest notified in 1954 Geology of Gloucestershire Cliffs of England River Severn {{England-SSSI-stub