Holleford
Key facts
- Country
- Canada
- Diameter
- 2.35 km
- Age
- about 550 ± 100 million years
- Location
- 44.47° N, 76.63° W
A faint, shallow, round hollow about 2 km across in farmland north of Kingston, Ontario. The crater is almost completely filled with younger sediment.
Holleford is a small, simple impact crater about 2.35 km across in farmland north of Kingston, in eastern Ontario, Canada. It was one of the first ancient impact craters to be found by deliberate search.
Discovery. In the early 1950s scientists of Canada's Dominion Observatory began examining aerial photographs of the Canadian Shield for round features that might be old craters. In 1955 they spotted a faint circular pattern of fields and woods near the village of Holleford. Gravity and magnetic surveys, and then drilling, showed a buried bowl filled with sediment, with broken rock beneath. Study of the drill cores later found quartz grains with shock features, confirming an impact.
What it hit. The impactor struck ancient crystalline rocks of the Grenville Province, gneiss and marble more than a billion years old. The bowl it dug was later flooded by the sea and filled with Cambrian and Ordovician sandstones and limestones, which protected it from erosion.
Age. The age is poorly known. The impact happened before the sea-floor sediments that fill the crater were laid down, so it is thought to be about 550 million years old, but with an uncertainty of about 100 million years.
Why it matters. Holleford helped prove that aerial photographs could reveal ancient craters, a technique that led to the discovery of many more. The impactor is unknown.
Visiting. The crater is on private farmland and is hard to see on the ground.
Did you know?
Holleford was spotted on aerial photographs in 1955.
Sea-floor sediments filled the crater and protected it from erosion.
It was one of the first ancient craters found by a deliberate search.