Aust Cliff

Aust Cliff is a cliff on the Severn Estuary in England, close to the village of Aust in South Gloucestershire. The 5.3-hectare site was notified in 1954 as a geological Site of Special Scientific Interest (SSSI). For visitors it is a place where rock layers tell a story more than 200 million years old, with one of Britain's best-known crossings in the background.

What makes Aust Cliff special?

The protection of the cliff rests on its fossil-bearing rock layers. The exposure is regarded as one of Britain's key Rhaetian localities, dating to the very end of the Triassic. Geological sources describe it as a prolific site for marine reptiles, mainly ichthyosaurs and plesiosaurs, along with rare dinosaur bones.

It is also known for the Rhaetic Bone Bed, which marks the base of the Westbury Formation within the Penarth Group. This thin layer packed with bone fragments is an important reference horizon for geologists studying the close of the Triassic in Britain.

What can you see in the rocks?

The cliff works as a readable cross-section through successive periods. At the bottom are the red marls and mudstones of the Mercia Mudstone Group, laid down under arid conditions. Above them lies the Blue Anchor Formation, followed by deposits of the Penarth Group and the Lias Group.

The Westbury Formation consists mostly of dark, carbon-rich shale with some sandstone and limestone containing shell debris. The colour change from red to dark grey reflects a shift from dry, arid land to shallow sea and lagoon settings. Even if you are not a geologist, it shows up as a clear, banded pattern in the cliff face.

The bridge above the cliff

The Severn Bridge crosses the cliff, carrying traffic over the estuary. The mix of a raw natural exposure and a major piece of engineering makes the area interesting for photography, especially when the light changes over the water at different times of day.

Planning a visit

• Location: by the village of Aust, South Gloucestershire, on the Severn Estuary shore.
• Nature of the site: protected for its geological value. Treat the rocks and fossils as scientific heritage and do not remove material without permission.
• Coordinates: roughly 51.60 N, 2.63 W.
• Before you go: the Severn Estuary has pronounced tides, so check local conditions and warnings before approaching the shoreline.

Frequently asked questions

Where is Aust Cliff? In England, near the village of Aust in South Gloucestershire, on the Severn Estuary.

How large is the site? It covers 5.3 hectares and has been a geological SSSI since 1954.

What fossils have been found here? According to geological sources, mainly marine reptiles such as ichthyosaurs and plesiosaurs, plus rare dinosaur bones.

What is the Rhaetic Bone Bed? A bone-rich layer that forms the base of the Westbury Formation in the Penarth Group.

Can you see the bridge? Yes, the Severn Bridge crosses the cliff, so it is part of the local landscape.