Rock Layers, K-T Boundary



		D1 Synorogenic Strata: This layer is composed of approximately 1,500 feet of alternating layers of sandstone from ancient river channels and mudstone from ancient flood plains. These layers were deposited during the early part of the uplift of the Front Range by rivers similar to the modern Platte River in northeastern Colorado. D1 Synorogenic Strata are coarse-grained along the Front Range and become fine-grained and coal-like to the east. These sediments were deposited in the Cretaceous Period and Paleocene Epoch (68-56 m.y.a). Typical fossils include petrified wood, leaves, dinosaur bones, and mammal teeth. K-T Boundary: The boundary between the Cretaceous (age of dinosaurs) and the Tertiary (age of mammals) Periods. This interval is often characterized by a half-inch-thick layer of debris that is the fallout from a massive comet or asteroid impact event in Mexico. The impact eject covered Earth with a mantle of dust and probably caused the extinction of the dinosaurs and their world.

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	A) Outcrop of the K-T boundary near Trinidad, Colorado. B) Fossil pollen grains allow us to recognize the K-T boundary because they identify plant species that change dramatically at the boundary.