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Mineralogic evidence for an impact event at the cretaceous-tertiary boundary

Science

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Abstract

A thin claystone layer found in nonmarine rocks at the palynological Cretaceous-Tertiary boundary in eastern Montana contains an anomalously high value of iridium. The nonclay fraction is mostly quartz with minor feldspar, and some of these grains display planar features. These planar features are related to specific crystallographic directions in the quartz lattice. The shocked quartz grains also exhibit asterism and have lowered refractive indices. All these mineralogical features are characteristic of shock metamorphism and are compelling evidence that the shocked grains are the product of a high velocity impact between a large extraterrestrial body and the earth. The shocked minerals represent silicic target material injected into the stratosphere by the impact of the projectile.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Mineralogic evidence for an impact event at the cretaceous-tertiary boundary
Series title:
Science
Volume
224
Issue:
4648
Year Published:
1984
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
867
Last page:
869
Number of Pages:
3