Stratigraphic, paleontologic, sedimentologic, and petrographic data are used to construct a revised system of correlation and stratigraphic nomenclature for Pennsylvanian and Permian rocks of central and northern Arizona and adjacent regions. The resulting scheme emphasizes major tectonic and depositional events but also provides for recognition of local to regional minor events. By recognizing stratigraphic spikes in the rock record and combining these with available biostratigraphic data, regional correlation is established in spite of a sparsity of fossils, complex cyclic lithologic units, abrupt facies changes, sporadic subsurface data, and drastic differences in quality and extent of outcrops.

Highlights of the proposed correlation and nomenclature include the following. 1. Differentiation of Supai and Naco Formations and restriction of use of the term "Supai." 2. Correlation of the Supai Group and the Hermit Formation into the western part of central Arizona (as far east as Sedona). 3. Formal definition of a new stratigraphic unit, the Schnebly Hill Formation, and several formal members. 4. Correlation of Pennsylvanian and Permian strata of the Grand Canyon and Defiance Plateau with rocks in central Arizona (Mogollon Rim and adjacent areas).

With a clearer concept of stratigraphy and nomenclature, the resulting sedimentologic and tectonic history of the region can be deciphered. The resulting interpretation of geologic history provides a foundation for relating tectonic and sedimentologic events of the Colorado Plateau to the evolution of southwestern North America.

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