The Chicxulub structure, in the subsurface of the northern Yucatán peninsulá, is a strong candidate to be the long-sought impact crater corresponding to the Cretaceous-Tertiary (K-T) boundary (Hildebrand et al., 1991). In two relatively recent articles some of us have described unusual clastic sediments from Arroyo el Mimbral in northeastern Mexico (Smit et al., 1992) and Deep Sea Drilling Project (DSDP) Sites 536 and 540 in the Leg 77 area of the Gulf of Mexico (Alvarez et al., 1992). We interpreted these clastic sediments as (1) the product of tsunami-generated water disturbances, (2) resulting from impact at Chicxulub, and (3) deposited precisely at the biostratigraphic K-T boundary. Subsequently, Keller et al. (1993) and Stinnesbeck et al. (1993) reported their own studies of the Mimbral and Leg 77 sites. They concluded (1) that the clastic sediments were not deposited by a tsunami event, (2) that they contain no evidence for a nearby impact, and (3) that they were not deposited at the biostratigraphic K-T boundary. We have chosen to stress in this Comment only the most fundamental problems we find in the three principal conclusions of Keller et al. and Stinnesbeck et al. An additional list of 18 detailed criticisms is available.   PDF