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Originally published in Science Express on 14 November 2002
Science 13 December 2002:
Vol. 298. no. 5601, pp. 2185 - 2188
DOI: 10.1126/science.1076249
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Reports

A Late Triassic Impact Ejecta Layer in Southwestern Britain

Gordon Walkden,1* Julian Parker,1 Simon Kelley2

Despite the 160 or so known terrestrial impact craters of Phanerozoic age, equivalent ejecta deposits within distal sedimentary successions are rare. We report a Triassic deposit in southwestern Britain that contains spherules and shocked quartz, characteristic of an impact ejecta layer. Inter- and intragranular potassium feldspar from the deposit yields an argon-argon age of 214 ± 2.5 million years old. This is within the age range of several known Triassic impact craters, the two closest of which, both in age and location, are Manicouagan in northeastern Canada and Rochechouart in central France. The ejecta deposit provides an important sedimentary record of an extraterrestrial impact in the Mesozoic that will help to decipher the number and effect of impact events, the source and dynamics of the event that left this distinctive sedimentary marker, and the relation of this ejecta layer to the timing of extinctions in the fossil record.

1 Department of Geology and Petroleum Geology, Kings College, University of Aberdeen, Aberdeen AB24 3UD, UK.
2 Department of Earth Sciences, Open University, Milton Keynes MK7 6AA, UK.
*   To whom correspondence should be addressed. E-mail: spherules{at}abdn.ac.uk

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
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Discovery of distal ejecta from the 1850 Ma Sudbury impact event.
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Sea-level change and facies development across potential Triassic-Jurassic boundary horizons, SW Britain.
S. P. Hesselbo, S. P. Hesselbo, S. A. Robinson, and F. Surlyk (2004)
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Uniquely extensive seismite from the latest Triassic of the United Kingdom: Evidence for bolide impact?.
M. J. Simms (2003)
Geology 31, 557-560
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