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Impact Crater, France |
The Rochechouart impact crater, west of Limoges in central France (general location in Google Maps), was created around 214 million years ago, during the late Triassic Period, by a large extraterrestrial body striking the Earth. In this now gentle landscape of woods and fields, evidence of the impact may be seen in disused and working quarries, and also in the distinctive stone used in many mediaeval and later buildings. The castle at Rochechouart, important in the wars between England and France in Richard the Lionheart's time, is built of impact breccia. Churches in nearby villages are built of glassy melt rocks (Figures 5, 7, 9) (see also Figure 15 - 17 on this link) produced by the impact (map of the crater and the breccias). The granitic rocks of the basement were extensively fractured and fragmented by the impact, and shatter cones (Figures 14 - 16) have been found.
It is now thought that the Rochechouart structure is just one of a chain of at least five impact craters formed when a fragmented comet hit the Earth (map). The images below show some of the features of the impact structure, and the fragmented and melted rocks produced by the impact.
If you visit Rochechouart, there is an excellent museum, Espace Metéorite Paul Pellas, at 16, rue Jean Parvy, the main street of the old town.
| Click on the images to enlarge | All images by Roger Suthren | |
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The chateau is itself built of the impact breccia. So are most of the buildings in this fortified mediaeval town. Before modern transport, builders used whatever suitable materials were locally available. |
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Whilst it is easy to work, the breccia used for frames and carvings has not proved very resistant to weathering over the centuries. |
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During rebuilding of the castle (15th century?), this problem was solved by using local granite for structural and ornamental components, such as these columns and arches. |
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The Rochechouart breccia consists largely of shattered fragments of the local igneous and metamorphic basement rocks. The fragments are seen clearly here in the walls of the chateau.
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Here is a sawn slice of the Rochechouart breccia. The holes represent soft fragments destroyed by weathering. |
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The church at Chassenon, built of impact rocks |
Part of the Roman complex of Cassinomagus, Chassenon, built of impact rocks. map |
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(above and right) close-ups of the impact rocks in Chassenon church. Note the presence of green, glassy suevite fragments. |
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(above) The church at Pressignac. Again, the main construction material is local impact rocks. (right) close-ups of the impact breccias used to build Pressignac church. Note the large gneiss fragment in the upper photo. Outcrops of impact rocks near the cemetery, seen in Streetview |
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This page is maintained by Roger Suthren. Last updated 30 November, 2022 4:48 PM
