Investigation of Cretaceous-Tertiary (K-T) boundary channel deposits in three sections in northeastern Mexico reveal three lithologically and mineralogically distinct units separated by three or more disconformities. The units include a spherule-rich layer (unit 1), laminated sandstone (unit 2), and rippled sand and shale layers (unit 3). On the basis of paleontological, mineralogical, and geochemical evidence, the K-T boundary is just above the top of unit 3. Although the deposits have previously been interpreted as a tsunami deposit related to a presumed K-T impact at Chicxulub on Yucatan, we have found no evidence of a nearby impact. We suggest that deposition occurred in an incised valley setting and over an extended period of time.
- Geological Society of America