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Navajo Sandstone is a geologic formation in the Glen Canyon Group that is spread across the U.S. states of southern Nevada, northern Arizona, northwest Colorado, and Utah as part of the Colorado Plateau province of the United States.〔Anonymous (2011b) (''Navajo Sandstone'' ), (Stratigraphy of the Parks of the Colorado Plateau ). U.S. Geological Survey, Reston, Virginia. last accessed August 18, 2013〕 The Navajo Sandstone formation is particularly prominent in southern Utah, where it forms the main attractions of a number of national parks and monuments including Red Rock Canyon National Conservation Area,〔(''Red Rock Canyon National Conservation Area - Rock Climbing.'' ) Southern Nevada District Office, Bureau of Land Management, Reno, Nevada〕 Zion National Park, Capitol Reef National Park, Glen Canyon National Recreation Area, Grand Staircase-Escalante National Monument, and Canyonlands National Park. Navajo Sandstone frequently overlies and interfingers with the Kayenta Formation of the Glen Canyon Group. Together, these formations can result in immense vertical cliffs of up to . Atop the cliffs, Navajo Sandstone often appears as massive rounded domes and bluffs that are generally white in color. ==Appearance and provenance== Navajo Sandstone frequently occurs as spectacular cliffs, cuestas, domes, and bluffs rising from the desert floor. It can be distinguished from adjacent Jurassic sandstones by its white to light pink color, meter-scale cross-bedding, and distinctive rounded weathering. The wide range of colors exhibited by the Navajo Sandstone reflect a long history of alteration by groundwater and other subsurface fluids over the last 190 million years. The different colors, except for white, are caused by the presence of varying mixtures and amounts of hematite, goethite, and limonite filling the pore space within the quartz sand comprising the Navajo Sandstone. The iron in these strata originally arrived via the erosion of iron-bearing silicate minerals. Initially, this iron accumulated as iron-oxide coatings, which formed slowly after the sand had been deposited. Later, after having been deeply buried, reducing fluids composed of water and hydrocarbons flowed through the thick red sand which once comprised the Navajo Sandstone. The dissolution of the iron coatings by the reducing fluids bleached large volumes of the Navajo Sandstone a brilliant white. Reducing fluids transported the iron in solution until they mixed with oxidizing groundwater. Where the oxidizing and reducing fluids mixed, the iron precipitated within the Navajo Sandstone. Depending on local variations within the permeability, porosity, fracturing, and other inherent rock properties of the sandstone, varying mixtures of hematite, goethite, and limonite precipitated within spaces between quartz grains. Variations in the type and proportions of precipitated iron oxides resulted in the different black, brown, crimson, vermillion, orange, salmon, peach, pink, gold, and yellow colors of the Navajo Sandstone. The precipitation of iron oxides also formed laminea, corrugated layers, columns, and pipes of ironstone within the Navajo Sandstone. Being harder and more resistant to erosion than the surrounding sandstone, the ironstone weathered out as ledges, walls, fins, "flags", towers, and other minor features, which stick out and above the local landscape in unusual shapes.〔Chan, MA, and WT Parry (2002) (''Mysteries of Sandstone Colors and Concretions in Colorado Plateau Canyon Country.'' PDF version, 468 KB ) Public Information Series no. 77. Utah Geological Survey, Salt Lake City, Utah.〕〔Chan, M., BB Beitler, WT Parry, J Ormo, and G Komatsu (2005) (''Red Rock and Red Planet Diagenesis: Comparison of Earth and Mars Concretions.'' PDF version, 3.4 MB ). GSA Today. vol. 15, no. 8, pp. 4–10.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Navajo Sandstone」の詳細全文を読む スポンサード リンク
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