New dating moves Oklahoma’s Ames impact crater 100 million years closer to a mass extinction
Researchers at the University of Texas at Austin date the buried Ames impact structure to about 370 million years ago, rather than the roughly 467-million-year-old Ordovician event it was long linked to. The revised timing places the impact near the Late Devonian marine extinction, but the study does not show that the impact caused it.
Bottom line — If confirmed, the 370-million-year date would remove Ames from the Ordovician impact cluster and place it near the Late Devonian extinction.
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The new estimate comes from uranium-lead dating of zircon crystals in impact-melted rock; the Times of India reports one analysis found an age of 369.7 million years, with an uncertainty of about 5.9 million years.
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The Times of India says the earlier age relied on a small amount of fossil-bearing material, including conodont teeth; the researchers argue older fossils could have been excavated and redeposited by the impact.
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The University of Texas team says the revised date puts Ames near the Frasnian-Famennian boundary and the Upper Kellwasser Crisis, which affected marine life.
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Space.com notes that the impact alone was not large enough to cause a mass extinction; reduced ocean oxygen, super-volcanism and other events are among the possible contributing factors.
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The Oklahoman reports the crater helped lead to oil and gas discoveries after it was identified in 1991; the buried structure lies beneath about 2.7 kilometres of rock, according to Space.com.
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The Times of India reports that limited rock samples from Ames make it difficult to obtain more suitable zircon grains, so additional material could help test the new interpretation.