DEPOSITION OF CHANNEL DEPOSITS NEAR THE CRETACEOUS-TERTIARY BOUNDARY IN NORTHEASTERN MEXICO - CATASTROPHIC OR NORMAL SEDIMENTARY DEPOSITS

Investigation of Cretaceous-Tertiary (K-T) boundary channel deposits i n three sections in northeastern Mexico reveal three lithologically an d mineralogically distinct units separated by three or more disconform ities. The units include a spherule-rich layer (unit 1), laminated san dstone (unit 2), and rippled sand and shale layers (unit 3). On the ba sis of paleontological, mineralogical, and geochemical evidence, the K -T boundary is just above the top of unit 3. Although the deposits hav e previously been interpreted as a tsunami deposit related to a presum ed K-T impact at Chicxulub on Yucatan, we have found no evidence of a nearby impact. We suggest that deposition occurred in an incised valle y setting and over an extended period of time.