Fig. 25

The Kaibab Formation, the cap rock of the Grand Canyon, the youngest Paleozoic rock unit on the southern Colorado Plateau, is composed of a variety of lithologic types that were deposited within a complex shallow-marine setting during the Permian. Marine invertebrate fossils are abundant in the Kaibab Formation. Brachiopods, fenestrate and ramose bryozoans, crinoids, siliceous sponges, and solitary corals are commonly found in western sections. Fragments of trilobites, ostracods, foraminifers, and molluscs are rare. In eastern sections, molluscan fauna characterized by pelecypods and poorly preserved gastropods dominate. Lateral change in faunal assemblages reflects a shoreward transition to increasingly restricted-marine environments. Shallow-water, low-energy levels, limited water circulation, elevated temperature, and salinity characterize these environments. An important note is that many of the fossil forms in the Kaibab Formation became extinct toward the end of the Permian (e.g., trilobites).

Fig. 26 - Fossil types representitve of the Kaibab Formation. From left to right: coiled gastropd (Bellerophontid), solitary rugose coral, productid brachiopod (Derbyia), and productid brachiopod (Peniculauris bassi).