The famous iridium-enriched Cretaceous -- Paleogene boundary , which separates the Cretaceous from the Cenozoic , occurs as a discontinuous but distinct thin marker bedding above and occasionally within the formation , near its boundary with the overlying Fort Union Formation .
The famous iridium-enriched Cretaceous -- Palaeogene boundary , which separates the Cretaceous from the Cenozoic , occurs as a distinct thin marker bedding above and occasionally within the formation , near its boundary with the overlying Fort Union Formation .