Woodleigh
Key facts
- Country
- Australia
- Diameter
- 60 km
- Age
- 364 ± 8 million years
- Location
- 26.05° S, 114.67° E
Nothing: the structure is buried beneath the flat sheep country east of Shark Bay, Western Australia.
Woodleigh is a large buried impact structure in Western Australia, beneath Woodleigh station east of Shark Bay. Its size is debated: estimates range from about 60 km to more than 120 km across, which, at the larger end, would make it one of the biggest impact structures on Earth.
Discovery. A borehole drilled in the late 1970s happened to strike the structure's central uplift, but its meaning was not understood. In 1997 a gravity survey showed a large round pattern centred on the area, and in 1999 geologists drilled a new core. In April 2000 they announced that it was an impact structure.
Proof of impact. The core contains breccia, veins of melted glassy rock and quartz with planar deformation features, formed only at shock pressures far beyond anything other than a large impact. In 2018 scientists reported reidite, a rare, extremely dense form of zircon produced only at very high pressure, in the central uplift, which supports a large size.
What it hit. The impactor struck ancient crystalline basement rocks beneath a cover of Palaeozoic sediments of the Carnarvon Basin. The central uplift is about 20 km across.
Age and extinction. Early estimates placed the impact between about 260 and 200 million years ago, but more recent dating gives about 364 million years, in the Late Devonian. This is close to the time of the Late Devonian mass extinctions, and some scientists have suggested a connection. The link is unproven.
Why it matters. Woodleigh shows how a giant crater can hide beneath a flat landscape. The impactor is unknown.
Did you know?
Woodleigh may be more than 120 km across, though estimates vary widely.
A borehole hit its central uplift in the 1970s, decades before anyone knew it was a crater.
Reidite, a rare high-pressure form of zircon, has been found in its core.