Second Day: Early and Middle Triassic Stratigraphy, Paleontology and Correlation in Northeastern Arizona

Today’s trip traverses a nearly east-west swath of the southern Colorado Plateau in northeatern Arizona (Fig. 2.1), where the low and barren topography is developed in Permian and Triassic sedimentary rocks. Here, our focus is on the Lower-Middle Triassic Moenkopi Formation. In northern Arizona, east of Flagstaff, the Moenkopi section (Fig. 2.2) is a relatively thin (< 150 m thick) and almost entirely nonmarine section of a normally much thicker and mixed marine-nonmarine lithosome that crops out from New Mexico-Arizona through Utah-Colorado into WyomingMontana. However, most of the nonmarine fossil record of the Moenkopi Formation (Group) comes from northeastern Arizona—megafossil plants, conchostracans, trace fossils (notably tetrapod tracks) and vertebrate body fossils (Table 2.1). These are fossils of Early Triassic (Nonesian/Spathian) and Middle Triassic (Perovkan/Anisian) age. Similarly, most of the published magnetostratigraphy of the Moenkopi is based on sampling in northeastern Arizona. Finally, the Moenkopi outcrops here provide us with an excellent opportunity to examine basinwide unconformities and regional lithostratigraphic correlation of the Moenkopi backed up by sequence stratigraphy, biostratigraphy and magnetostratigraphy.