Kentland
Key facts
- Country
- United States
- Diameter
- 7 km
- Age
- less than about 97 million years
- Location
- 40.75° N, 87.40° W
Almost nothing at the surface, which is flat farmland. The central uplift is exposed in a large working limestone quarry near Kentland, Indiana, where rock layers stand on end.
Kentland is an impact structure about 7 km across in north-western Indiana, in the United States. Almost all of it is hidden under glacial deposits and farmland, but a large quarry cuts into its centre, exposing one of the most dramatic displays of disturbed rock in the Midwest.
What it hit. The target was a thick layer cake of Palaeozoic sedimentary rocks. In the centre of the structure, layers of Ordovician limestone and dolomite were lifted several hundred metres above their normal position and tilted until they stand vertically or are even overturned. The age of the impact is uncertain; it happened after the youngest rocks affected were laid down, and is usually given as less than about 97 million years.
The birthplace of shatter cones. Kentland has a special place in the history of impact science. In the 1940s the American geologist Robert Dietz studied the shatter cones in the quarry, cone-shaped fractures with branching grooves. He argued that they could only form when a powerful shock wave passed through rock, and that they were therefore evidence of an impact. His idea was later confirmed, and shatter cones are now one of the standard field tests for recognising impact structures worldwide. Quartz grains with shock features have also been found at Kentland.
Why it matters. Kentland helped give geologists one of their most important tools for finding ancient impacts.
Visiting. The quarry is a working industrial site and is private. Entry is only possible with the owner's permission, and quarry faces are dangerous: never approach them without proper guidance and safety equipment.
Did you know?
Shatter cones were first recognised as impact evidence from rocks at Kentland in the 1940s.
Rock layers in the quarry have been tilted until they stand on end.
Most of the structure is hidden under glacial deposits.