Shocked Quartz Grains in Rhyolitic Bentonites

摘要

A classical conflict still exists between geologists that explain mass extinctions by meteoritic impacts, and those that involve only earthly causes. The two largest extinctions (the Permo-Triassic and the Cretaceous-Tertiary) have both been suggested to have been caused by impacts. At Meishan, underlying the Permo-Triassic black clay horizon (Bed 26) is a rhyolitic bentonite (Bed 25) which can be followed across the whole of southern China. No shocked quartz grains have been found in any of the many samples of this bed we have studied over the years.