Iridium concentration and noble gas composition of Cretaceous—Tertiary boundary clay from Stevns Klint, Denmark

摘要

The Cretaceous-Tertiary (K-T) boundary about 65 million years ago records a mass extinction event caused by abolide impact. K-T boundary clay collected from Stevns Klint, Denmark was investigated in this work. Iridium concen-trations of eight clays across the K-T boundary were determined using a multiple gamma-ray analysis system after neu-tron activation. Anomalously high Ir concentrations were detected in five marl samples, with the highest concentrationbeing 29.9 ppb. Four samples were analyzed for all noble gases. No extraterrestrial Ar, Kr, and Xe were discovered in anyof the samples, although most of the 3He which was detected was extraterrestrial. Solar-like Ne was observed only in thesample SK4, which had an Ir concentration of 14.3 ppb, indicating the presence of micrometeorites. The solar-like Neclearly did not originate from an asteroid/comet associated with the bolide impact, as that asteroid is thought to have beenextremely large. Also, because there was no sign of a high accretion rate of micrometeorites at the boundary it could notbe ascertained whether the solar-like Ne was related to a catastrophic event that led to the extinction of the dinosaurs.