Abstract

Spectacular color variations in the Lower Jurassic Navajo Sandstone reflect stratigraphic and structural control on the spatial distribution of fluid-driven alteration. Field observations and supervised classification of Landsat 7 Enhanced Thematic Mapper (ETM+) satellite imagery show that the most extensive regional bleaching of the Navajo Sandstone occurs on eroded crests of Laramide uplifts on the Colorado Plateau in southern Utah. Alteration patterns suggest that the blind reverse faults that core the eastern monoclines associated with these uplifts were carriers for hydrocarbons and brought the buoyant fluids to the crests of monoclines and anticlines, where they bleached the sandstone in both structural and stratigraphic traps. The extent of bleaching indicates that the Navajo Sandstone (Navajo Sandstone, Aztec Sandstone, and Nugget Sandstone) may have been one of the largest hydrocarbon reservoirs known. Rapid incision and breaching of this reservoir during Tertiary uplift and erosion of the Colorado Plateau could have released enough carbon into the atmosphere to significantly contribute to global carbon fluxes and possibly influence climate.

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