Abstract

The Permian System of the Colorado Plateau contains a variety of marine and continental sedimentary rocks deposited during Wolfcampian and Leonardian time. In southwestern Colorado and southeastern Utah the system is largely arkosic redbeds which become finer-grained and segregated into distinctive units southwestward from the source area of the Uncompahgre uplift. The redbeds were deposited on arid coastal plains closely related to shallow marine environments along the southern and western margins of the province. The removal of clastics from the source area was almost complete by the close of Wolfcamp time, for Leonardian deposits consist of eolian sandstones of wide lateral extent in the Four Corners region and marine sandstones, carbonates, and evaporites along the southern and western plateau. Continuous sedimentation probably occurred across the Pennsylvanian-Permian temporal boundary along the margin of Uncompahgre source area and in the San Juan and Black Mesa basins of New Mexico and Arizona. Many local areas were positive during Pennsylvanian time, but were buried by early Permian or slightly older sedimentation. Most of southeastern Utah was subjected to late Pennsylvanian or early Permian erosion that was related to intense bevelling of the Emery and Defiance uplifts where the Pennsylvanian was entirely removed. A previously used term "Rico formation" is abandoned because it is neither useful nor mappable. Coarse clastics of the undifferentiated Cutler Group were derived entirely from the Uncompahgre uplift, and grade laterally into the finer-grained lower Cutler in the Four Corners area, the Abo Formation of central New Mexico, and the Supai Formation of northern Arizona. The lower Cutler redbeds grade westward into the lower Halgaito redbeds, and interfinger with the overlaying near-shore marine Cedar Mesa Sandstone. The lower Cutler and Halgaito clastics interfinger with marine carbonates toward the NW. The Wolfcampian carbonates are designated the Elephant Canyon Formation in this report. The Supai Formation of the Grand Canyon represents the Halgaito and Cedar Mesa formations, but the 2-fold distinction in the Supai (restricted) of E.-central Arizona is not apparent. The equivalent Supai and Abo formations interfinger with marine carbonates toward the S. and W. Lateral equivalents of the upper Cutler are the Organ Rock-Hermit redbeds, and the overlying eolian to marine De Chelly Sandstone. The Organ Rock- Hermit shales are restricted to the Four Corners- Monument Valley-Grand Canyon areas. The De Chelly Sandstone, the youngest Permian deposits of the central Colorado Plateau, are eolian over most of the province, but grade to marine sandstones along the southern extremes of the plateau. It is recommended that equivalent sandstones in E. -central Arizona (formerly the upper Supai Formation) and central New Mexico (formerly the Meseta Blanca Member of the Yeso Formation) be referred to the De Chelly Sandstone of Leonardian (?) age. Post-Cutler (post-De Chelly) sedimentation was restricted to the southern and western margins of the plateau. The oldest of these deposits, the Yeso Formation (restricted) is a mixed marine association of carbonates, evaporites, and clastics that extends across the southern part of the Colorado Plateau. The overlying Coconino-Glorieta sandstone is a shallow marine deposit in central New Mexico (Glorieta) that grades westward into thick eolian deposits (Coconino). The youngest Permian deposits on the plateau are the San Andres Formation of central New Mexico, and the equivalent Kaibab-Toroweap formations of northern Arizona and the western margin of the province in Utah. These sediments are largely shallow marine carbonates and clastics, with local occurrences of evaporites. An epeirogenic uplift occurred sometime during late Permian or early Triassic time, but the amount and time of uplift was not great,for only relatively minor erosional features are known. The time lapse represented by the disconformity is the upper half of the Permian and the lowermost Triassic, but erosion took place late enough to allow thorough lithification of Permian sediments. The climate of the province was arid or semi-arid during Permian time, as shown by the preservation of red beds and fresh feldspar detritus, and the presence of vast dune deserts and extensive evaporite deposits throughout the system.

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