New Mexico Geological Society Annual Spring Meeting — Abstracts

Extensive geochronologic studies of the rocks adjacent to the Cretaceous-Tertiary (K-T) interface in the San Juan Basin have now provided compelling data attesting to the Paleocene age of the dinosaur-bearing Ojo Alamo Sandstone in New Mexico and the Animas Formation in Colorado. These data consist of radiometric age determinations for Cretaceous strata underlying the K-T interface and palynologic, paleomagnetic, and geochemical evidence attesting to the Paleocene age of the strata above the K-T interface. The identification of the paleomagnetic normal interval - C29n - in the dinosaur-bearing lower part of the Ojo Alamo Sandstone in the southern San Juan Basin at multiple localities allows for the precise dating of the last occurrence of Paleocene dinosaurs at the top of chron C29n at 64.432 Ma.

The conventional wisdom (entrenched dogma) among most geologists, and especially among vertebrate paleontologists has been, for more than 100 years, that all dinosaurs became extinct at the end of the Cretaceous. Thus, dinosaur bone found in place in a formation provided indisputable evidence that the formation was Cretaceous in age. Now, with the discovery of Paleocene dinosaurs, the paradigm of Cretaceous-only dinosaurs must shift. Let us hope that this paradigm-shift will be a smooth and placid lateral-slip along planar fault blocks rather than a grumbling, rumbling, herky-jerky sliding of jagged-edged, opposing sides past each other. Science must always be conservative and accept such paradigm shifts only on the basis of the most solid evidence, however, when the data do finally speak, the shift must be accepted by all of us who follow the data in the noble pursuit of finding out how the world was made.