Navajo Sandstone

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A prominent cuesta of Navajo Sandstone rims the edge of the San Rafael Swell in eastern Utah.
A prominent cuesta of Navajo Sandstone rims the edge of the San Rafael Swell in eastern Utah.

Navajo Sandstone is a geologic formation in the Glen Canyon Group that is spread across the U.S. states of northern Arizona, northwest Colorado, Nevada, and Utah (the unit is not part of a group in Nevada). It is located in the Colorado Plateau province of the United States. This rock formation is particularly prominent in southeastern Utah, where it forms the main attractions of a number of national parks and monuments including Zion National Park, Capitol Reef National Park, the Grand Staircase-Escalante National Monument, and Canyonlands National Park. Navajo sandstone frequently occurs above the Kayenta Formation and Wingate Sandstone (all three formations are in the same group). Together, these three formations can result in immense vertical cliffs of 2000 feet or more. Atop the cliffs, Navajo sandstone often appears as massive rounded domes and bluffs that are generally white in color.

Because of its widespread occurrence, unique appearance, and dramatic outcrops, the Navajo sandstone is one of the most famous rock formations in the world.

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[edit] Appearance and Provenance

Navajo 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, i.e. crimson, vermillion, orange, salmon, peach, pink, gold, yellow, and white exhibited by the Navajo Sandstone reflect a long history of alteration of it 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 originally came from the break down by weathering of iron-bearing silicate minerals. Initially, the iron accumulated as iron-oxide coatings, which formed slowly after the sand had been deposited. Later, after having been deeply buried, reducing fluids, i.e. water containing 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 iron oxides precipitated resulted in the different 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[1][2].

[edit] Age and history of investigation

The age of this rock unit is somewhat controversial. It may originate from the Late Triassic but is at least as old as the Early Jurassic stages Pliensbachian and Toarcian.[3] There is no type locality of the name. It was simply named for the 'Navajo Country' of the southwestern United States.[4] The two major subunits of the Navajo are the Lamb Point Tongue (Cedar City area) and the Shurtz Sandstone Tongue (Kanab area).[5].

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.[6] Its age was modified again by Padian in 1989.

[edit] Places found

Navajo Sandstone outcrops are found in these geologic locations:

The formation is also found in these parklands (incomplete list):

[edit] Iron oxide concretions (Moqui marbles)

The Navajo Sandstone is also well known among rockhounds, planetary geologists, and practitioners of New Age religions for the hundreds of thousands of iron oxide concretions. They are believed to represent an extension of Hopi Native American traditions regarding ancestor worship ("moqui" translates to "the dead" in the Hopi language). Informally, they are called "Moqui marbles" after the local proposed Moqui native American tribe (they have alternately been called "Moqui balls," "Moki marbles," "shaman stones" or "thunderballs" by various enthusiasts[7]). Thousands of these concretions weather out of outcrops of the Navajo Sandstone within south-central and southeastern Utah within an area extending from Zion National Park eastward to Arches and Canyonland national parks. They are quite abundant within Grand Staircase-Escalante National Monument [8][9].

The iron oxide concretions found in the Navajo Sandstone exhibit a wide variety of sizes and shapes. Their shape ranges from spheres to discs; buttons; spiked balls; cylindrical hollow pipe-like forms; and other odd shapes. Although many of these concretions are fused together like soap bubbles, many more also occur as isolated concretions, which range in diameter from the size of peas to baseballs. The surface of these spherical concretions can range from being very rough to quite smooth. Some of the concretions are grooved spheres with ridges and grooves around their circumference [10][11].

The abundant concretions found in the Navajo Sandstone consist of sandstone cemented together by hematite (Fe2O3), and goethite (FeOOH). The iron forming these concretions came from the break down of iron-bearing silicate minerals by weathering to form iron oxide coatings on other grains. During later diagenesis of the Navajo Sandstone while deeply buried, reducing fluids, likely hydrocarbons, dissolved these coatings. When the reducing fluids containing dissolved iron mixed with oxidizing groundwater, they and the dissolved iron were oxidized. This caused the iron to precipitate out as hematite and goethite to form the innumerable concretions found in the Navajo Sandstone. These concretions are regarded as terrestrial analogues of the hematite spherules, called alternately Martian "blueberries" or more technically Martian spherules, which the Opportunity rover found at Meridiani Planum on Mars [12][13].

[edit] References

[edit] Works cited

  • Averitt, P., Wilson, R.F., Detterman, J.S., Harshbarger, J.W. and Repenning, C.A., 1955, "Revisions in correlation and nomenclature of Triassic and Jurassic formations in southwestern Utah and northern Arizona", American Association of Petroleum Geologists Bulletin, v. 39, no. 12, p. 2515-2524
  • Baker, A.A., 1936, "Geology of the Monument Valley-Navajo Mountain region, San Juan County, Utah", U.S. Geological Survey Bulletin 865, 106 p., Also, U.S. Geological Survey Oil and Gas Investigations Map OM-168, and Bulletin 1087-D.
  • Gregory, H.E. and Stone, R.W., 1917, "Geology of the Navajo country; a reconnaissance of parts of Arizona, New Mexico, and Utah", U.S. Geological Survey Professional Paper, 93, 161 p.
  • Chan, M.A. and W.T. Parry, 2002, Mysteries of Sandstone Colors and Concretions in Colorado Plateau Canyon Country PDF version, 468 KB Utah Geological Survey Public Information Series 77:1-19.
  • Chan, M.A., B.B. Beitler, W.T. 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, v. 15, n. 8, pp. 4-10.
  • Lewis, G.E., Irwin, J.H. and Wilson, R.F., 1961, "Age of the Glen Canyon Group (Triassic and Jurassic) on the Colorado Plateau", Geological Society of America Bulletin v. 72, no. 9, p. 1437-1440
  • Padian, K., 1989, "Presence of dinosaur Scelidosaurus indicates Jurassic age for the Kayenta Formation (Glen Canyon Group, northern Arizona)", Geological Society of America, Geology, v. 17, no. 5, p. 438-441
  • Poole, F.G. and Stewart, J.H., 1964, "Chinle Formation and Glen Canyon Sandstone in northeastern Utah and northwestern Colorado, IN Geological Survey research 1964", U.S. Geological Survey Professional Paper, 501-D, p. D30-D39
  • USGS: Colorado River Basin Stratigraphy - Navajo Sandstone Accessed 18 March 2006 (public domain text)

[edit] Notes

  1. ^ Chan and Parry 2002
  2. ^ Chan and others, 2005
  3. ^ USGS Accessed 18 March 2006
  4. ^ Gregory, 1917
  5. ^ Averitt and others, 1955
  6. ^ Poole and Stewart, 1964
  7. ^ [1]
  8. ^ Chan and Parry 2002
  9. ^ Chan and others, 2005
  10. ^ Chan and Parry 2002
  11. ^ Chan and others, 2005
  12. ^ Chan and Parry 2002
  13. ^ Chan and others, 2005

[edit] Further reading

[edit] Internet - general

[edit] Scientific publications

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