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Science 8 May 1987:
Vol. 236. no. 4802, pp. 705 - 709
DOI: 10.1126/science.236.4802.705
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Articles

Shocked Quartz in the Cretaceous-Tertiary Boundary Clays: Evidence for a Global Distribution

BRUCE F. BOHOR 1, PETER J. MODRESKI 1, and EUGENE E. FOORD 1

1 U.S. Geological Survey, Box 25046, Denver, CO 80225.

Shocked quartz grains displaying planar features were isolated from Cretaceous- Tertiary boundary clays at five sites in Europe, a core from the north-central Pacific Ocean, and a site in New Zealand. At all of these sites, the planar features in the shocked quartz can be indexed to rational crystallographic planes of the quartz lattice. The grains display streaking indicative of shock in x-ray diffraction photographs and also show reduced refractive indices. These characteristic features of shocked quartz at several sites worldwide confirm that an impact event at the Cretaceous-Tertiary boundary distributed ejecta products in an earth-girdling dust cloud, as postulated by the Alvarez impact hypothesis.

Submitted on November 3, 1986
Accepted on February 20, 1987


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