The Colorado Plateau

1. The Colorado Plateau By Ryan

2. How it Began • The Sauk Transgression in the Cambrian • Regression during the Ordovician, exposing the Mauv limestone to erosion, causing a major unconformity • During the Silurian, Ordovician glaciers began to melt causing another transgression (Tippecanoe) • During the Mississippian, deepening of the water saw deposition of Redwall Limestone

3. The Beginning… • A drop in the water level during the late Mississippian caused erosion of the Redwall Limestone • From the Pennsylvanian to Permian all of the deposition occurred in a beach, or lagoon environment. • The final units, The Toroweap and Kaibab limestone were deposited in a marine environment, made possible by the Absaroka transgression • These transgressions, regressions, erosions resulted in 21 distinct, mostly sedimentary layers

4. Ages of the Colorado Plateau • Cenozoic – The youngest of the rock ages • Identified by fossilized mammals • Mesozoic – Middle age rocks • Identified by dinosaur fossils • Paleozoic – Old rocks • Identified by early fossilized fish • Pre-Cambrian - Ancient rocks • Identified by fossilized bacteria

5. Rock Layers and Descriptions Mesozoic Rock layers – Terrestrial rocks, made of soft colorful sandstones and shale's. Deposited in shallow marine environments Paleozoic Rock layers – Hard limestone's deposited in deep marine environments Precambrian Rock – Basement rock of the Colorado River. Made of Gneisses and volcanic igneous rock intrusions

7. Common Fossils and Ages of the Region • Precambrian fossils are limited to Stromatilites • The next 3 layers,(Tapeats Sandstone, Bright Angel Shale, and Mauv Limestone) contain ocean going invertebrates. Ex. Brachiopods, clams, trilobites, corals, and worms. • Redwall Limestone and Supai layers contain more marine fossils, and Bryozoans, Crinoids, and Foraminifera's

8. Fossils Continued • From the Supai to the Coconino layers there are no fossilized bones, but there are many trace fossils • Toroweap limestone contains some sponges, and a few other single cellular organisms • Kaibab contains a few different species of fish teeth

9. Environmental Forces Acting on Grand Canyon • Erosion- This is the most powerful force acting on the canyons of the Colorado Plateau. • Erosion by water and ice is the most common • Wind erosion is the next most prevelant

10. The Colorado River and Erosion The water that runs off of the cliffs and ledges runs into the Colorado River carrying all of the sediment that wasn’t secured by surface plant life. This means all of that sediment hits the river and acts like a liquid saw cutting its’ way through the canyon.

11. Ice Erosion, How? • Ice erosion occurs mostly on the North Rim of the Grand Canyon. • Ice erodes the rock by penetrating the rock as water. • Once in the cracks and crevices of the canyon, low temps freeze the water. • The expansion of the water to ice causes the rocks to break and fall into the canyon, and the river bellow.

12. Wind Erosion, 2nd only to Water • Begins like water by picking up loose sediment from the dry desert floor. • Differs because, not only does the wind deposit the sediment into the river, but it throws the sediment into the canyon walls • The effect is the same, this can cause rock slides or other erosive activity

13. The Result of Erosion