PROXIMAL CRETACEOUS-TERTIARY BOUNDARY IMPACT DEPOSITS IN THE CARIBBEAN

Trace element, isotopic, and mineralogic studies indicate that the proposed impact at the Cretaceous-Tertiary (K-T) boundary occurred in an ocean basin, although a minor component of continental material is required. The size and abundance of shocked minerals and the restricted geographic occurrence of the ejecta layer and impact-wave deposits suggest an impact between the Americas. Coarse boundary sediments at sites 151 and 153 in the Colombian Basin and 5- to 450-meter-thick boundary sediments in Cuba may be deposits of a giant wave produced by a nearby oceanic impact. On the southern peninsula of Haiti, a ∼50-centimeter-thick ejecta layer occurs at the K-T boundary. This ejecta layer is ∼25 times as thick as that at any known K-T site and suggests an impact site within ∼1000 kilometers. Seismic reflection profiles suggest that a buried ∼300-km-diameter candidate structure occurs in the Colombian Basin.