The Navajo Sandstone is a geological 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.
Description
The Navajo Sandstone is particularly prominent in southern Utah, where it forms the main attractions of a number of national parks and monuments including Arches National Park, Zion National Park, Capitol Reef National Park, Canyonlands National Park, Glen Canyon National Recreation Area, and Grand Staircase–Escalante National Monument. 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 2,200 feet (670 m). 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 laminae, 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.
Age and history of investigation The age of the Navajo Sandstone is somewhat controversial. It may originate from the Late Triassic but is at least as young as the Early Jurassic stages Pliensbachian and Toarcian. There is no type locality of the name. It was simply named for the 'Navajo Country' of the southwestern United States. The two major subunits of the Navajo are the Lamb Point Tongue (Kanab area) and the Shurtz Sandstone Tongue (Cedar City area). The Navajo Sandstone was originally named as the uppermost formation of the La Plata Group by Gregory and Stone in 1917. Baker reassigned it as the upper formation of Glen Canyon Group in 1936. Its age was modified by Lewis and others in 1961. The name was originally not used in northwest Colorado and northeast Utah, where the name 'Glen Canyon Sandstone' was preferred. A 2019 radioisotopic analysis suggests that the Navajo Sandstone formation dates to the early Jurassic and began around 200-195 million years ago. Kevin Padian stated in 1989 that the Navajo Sandstone extended into the Toarcian Stage.
Depositional environment The sandstone was deposited in an arid erg on the Western portion of the Supercontinent Pangaea. This region was affected by annual monsoons that came about each winter when cooler winds and wind reversal occurred.
Outcrop localities
Navajo Sandstone outcrops are found in these geologic locations:
Colorado Plateau Black Mesa Basin Great Basin province Paradox Basin Piceance Basin Plateau Sedimentary Province San Juan Basin Uinta Basin Uinta Uplift Uncompaghre Uplift The formation is also found in these parklands (incomplete list):
Glen Canyon National Recreation Area Grand Staircase–Escalante National Monument Zion National Park Canyonlands National Park Capitol Reef National Park Arches National Park Dinosaur National Monument Navajo National Monument Colorado National Monument Coral Pink Sand Dunes State Park, Kanab, Utah
Vertebrate paleofauna
Ornithodires Indeterminate theropod remains geographically located in Arizona, USA. Theropod tracks are geographically located in Arizona, Colorado, and Utah, USA. Ornithischian tracks located in Arizona, USA.
Iron oxide concretions
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