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

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