Geochemisty at DSDP Hole 62-465A

Very significant enhancements of the element iridium have been observed in association with the Cretaceous/ Tertiary boundary in marine sediments laid down 65 m.y. ago and subsequently uplifted above the ocean's surface. If our hypothesis for the origin of the iridium and the cause of the Cretaceous/Tertiary life extinctions (the asteroid-impact theory) (Alvarez et al., 1980) is correct, the Ir anomaly should be associated with the Cretaceous/ Tertiary boundary region wherever it is intact. The present work was undertaken to search for the Ir anomaly in a deep-sea-drilling core, in order to check this aspect of the asteroid-impact theory.

(Table 1) Elemental abundances in DSDP Core 86-577B-1

An Ir anomaly of 61 ng/cm**2 was found in Deep Sea Drilling Project Hole 577B at the same stratigraphic level as the Cretaceous/Tertiary boundary defined by nannoplankton. This close correspondence supports the asteroid-impact theory for the Cretaceous/Tertiary boundary extinctions.