Stratigraphic, mineralogical, chemical and isotopic evidence have led to the large (˜10-km) asteroid or comet impact theory as the cause of the Cretaceous period coming to an end. However, a suitable crater has not yet been found. Although the crater may have been destroyed because half of what was then the ocean floor has since been subducted, researchers are still hot on the trail of the impact site(s).
A. R. Hildebrand and W. V. Boynton, Department of Planetary Sciences, University of Arizona, Tucson, believe that locating the original crater(s) would resolve the volcanism versus impact debate over what ended the Cretaceous period. Based on a large concentration of shocked mineral grains and the largest grains occurring in North America, and impact-wave deposits at the K/T boundary only from the Caribbean and southern North America, they suggest that the K/T boundary impact occurred between North and South America. They suggest the 300-km-diameter buried basement structure in the Columbia Basin as a possible K/T impact crater. The location of impact-wave deposits and possibly seismically triggered slumps also helped the two decide that impact(s) musthave occurred in the Caribbean region.