Abstract

Refined correlations and nomenclatural revisions of Pennsylvanian and Permian stratal units have resulted from geologic mapping and stratigraphic studies in the Sedona area, central Arizona. Among keys to the regional stratigraphy are the following features. A purplish mudstone and limestone unit (Early? and Middle Pennsylvanian), the most northwestern exposure of the lower member of the Naco Formation, is preserved locally at the base of the Pennsylvanian section. Above this is a sandstone and limestone member of the Naco Formation (Middle and Late? Pennsylvanian), formerly assigned to the lower member of the Supai Formation. A channeled unconformity separates the Naco from overlying conglomerate and sandstone members of the Supai Formation of Early Permian (Wolfcampian) age, formerly the middle member and the lower part of the upper member of the Supai Formation. A thin, parallel-bedded argillaceous sandstone, a southern and eastern facies of the Hermit Shale of the Grand Canyon of northern Arizona, overlies the redefined Supai, is regionally persistent, and is the basal unit of Leonard age. Red highly cross-bedded, cliff-forming sandstone overlies the Hermit, and in the eastern part of the Sedona area contains limestone and sandstone of the Fort Apache Member at the base. The Fort Apache Member and the overlying red crossbedded sandstone, formerly included in the upper member of the Supai, are here assigned to the Coconino Formation. A red-white color boundary within the cross-bedded cliff-forming sandstone is gradational and rises stratigraphically from west to east across the Sedona area. The color break is used to separate informal red and white sandstone members of the Coconino Formation. The units as now defined in the Sedona area correlate with units mapped in the Mogollon Rim of east-central Arizona, revealing regional facies relations and indicating that the mappable units are recognizable in outcrop as far east as the Fort Apache Indian Reservation.

Improved correlations have resulted that shed new light on the late Paleozoic history of central and northern Arizona. Strata of Early Pennsylvanian age are present in substantial thickness in the Grand Canyon of northern Arizona, but make up only a subordinate part of the Pennsylvanian section in central Arizona. In contrast, a comparatively thick section of Middle and Late Pennsylvanian strata in central Arizona is represented by a comparatively thin section of rocks in the Grand Canyon. The differences in thickness reflect differential movement between northern and central Arizona that occurred early in Middle Pennsylvanian time. Regional uplift terminated Pennsylvanian deposition in both northern and central Arizona. Following development of an irregularly channeled erosion surface, Early Permian (Wolfcampian) strata of the Esplanade Sandstone of the Supai Group of the Grand Canyon, and highly similar, correlative strata of the Supai Formation (restricted) of central Arizona, were deposited across the region. Aggradation waned, marked by the accumulation, early in Leonard time, of a thin blanket of argillaceous sandstone of the Hermit Formation. Renewed active aggradation is recorded in the Sedona area by accumulation of the red and white sandstone members of the Coconino Formation. The red sandstone member, bounded at the base by the Fort Apache Member, grades southeasterly into a limestone and siltstone member that contains sandstone in the upper part. The Supai and Hermit formations, and lower part of the Coconino Formation, as now recognized in the Sedona area, appear to correlate with members of the Cutler Formation of northeastern Arizona and the Four Corners area: the Supai with the Cedar Mesa Sandstone Member, the Hermit with the Organ Rock Member, and the red sandstone member of the Coconino with the DeChelly Sandstone Member.