Granby
Key facts
- Country
- Sweden
- Diameter
- 3 km
- Age
- about 470 million years
- Location
- 58.42° N, 14.93° E
Nothing obvious: farmland near Lake Vättern in Östergötland, southern Sweden. The crater is buried under younger sea-floor sediments.
Granby is a buried impact crater about 3 km across in Östergötland, southern Sweden, just east of Lake Vättern. It formed on the sea floor about 470 million years ago, in the Ordovician.
What it hit. The impactor struck a shallow sea floor of thin Cambrian and Ordovician sediments resting on ancient crystalline basement of the Baltic Shield. It dug a crater into the basement, and the sea then washed broken rock back into it before limestones buried it.
Proof of impact. The structure was revealed by geophysical surveys and drilling. In 2015 geologists reported quartz grains with planar deformation features, the microscopic fingerprint of shock, in breccia from the drill core, verifying an impact. Layers of sediment washed in by the returning sea, called resurge deposits, lie above the breccia.
A busy time for impacts. About 466 million years ago, a large asteroid broke up in the asteroid belt, and for millions of years afterwards far more meteorites and small asteroids reached the Earth than today. Granby is one of a group of Swedish craters, with Lockne, Målingen, Tvären and Hummeln, that formed around this time, and fossil meteorites from the same period are found in Swedish limestone quarries.
Why it matters. Granby adds to the evidence that the Ordovician meteorite shower produced many craters on Earth. The impactor is unknown.
Did you know?
Granby formed on the sea floor during the Ordovician meteorite shower.
Shocked quartz in a drill core verified the impact in 2015.
Fossil meteorites from the same period are found in Swedish limestone.