Red beds

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Cathedral Rock near Sedona, made of Permian redbeds Red Rock State Park, AZ.jpg
Cathedral Rock near Sedona, made of Permian redbeds
Red butte, Selja Gorges, Tunisia Red butte, Selja gorges, Tunisia.jpg
Red butte, Selja Gorges, Tunisia
Red beds of the Permo-Triassic Spearfish formation surround Devils Tower National Monument. Devils Tower aerial.jpg
Red beds of the Permo-Triassic Spearfish formation surround Devils Tower National Monument.

Red beds (or redbeds) are sedimentary rocks, typically consisting of sandstone, siltstone, and shale, that are predominantly red in color due to the presence of ferric oxides. Frequently, these red-colored sedimentary strata locally contain thin beds of conglomerate, marl, limestone, or some combination of these sedimentary rocks. The ferric oxides, which are responsible for the red color of red beds, typically occur as a coating on the grains of sediments comprising red beds. Classic examples of red beds are the Permian and Triassic strata of the western United States and the Devonian Old Red Sandstone facies of Europe. [1] [2]

Contents

Primary red beds

Primary red beds may be formed by the erosion and redeposition of red soils or older red beds, [3] but a fundamental problem with this hypothesis is the relative scarcity of red-colored source sediments of suitable age close to an area of red-bed sediments in Cheshire, England. Primary red beds may also form by in situ (early diagenetic) reddening of the sediment by the dehydration of brown or drab colored ferric hydroxides. These ferric hydroxides commonly include goethite (FeO-OH) and so-called "amorphous ferric hydroxide" or limonite. Much of this material may be the mineral ferrihydrite (Fe2O3 H2O). [4]

This dehydration or "aging" process has been found to be intimately associated with pedogenesis in alluvial floodplains and desert environments. Goethite (ferric hydroxide) is normally unstable relative to hematite and, in the absence of water or at elevated temperature, will readily dehydrate according to the reaction: [5]

2FeOOH (goethite)→ Fe2O3 (hematite) +H2O

The Gibbs free energy (G) for the reaction goethite → hematite (at 250 °C) is −2.76 kJ/mol and G becomes increasingly negative with smaller particle size. Thus detrital ferric hydroxides, including goethite and ferrihydrite, will spontaneously transform into red-colored hematite pigment with time. This process not only accounts for the progressive reddening of alluvium but also the fact that older desert dune sands are more intensely reddened than their younger equivalents. [6]

Diagenetic red beds

Red beds may form during diagenesis. The key to this mechanism is the intrastratal alteration of ferromagnesian silicates by oxygenated groundwaters during burial. Walker's studies show that the hydrolysis of hornblende and other iron-bearing detritus follows Goldich dissolution series. This is controlled by the Gibbs free energy of the particular reaction. For example, the most easily altered material would be olivine: e.g.

Fe2SiO4 (fayalite) + O2 → Fe2O3 (hematite) + SiO2 (quartz) with E = -27.53 kJ/mol

A key feature of this process, and exemplified by the reaction, is the production of a suite of by-products which are precipitated as authigenic phases. These include mixed layer clays (illite – montmorillonite), quartz, potassium feldspar and carbonates as well as the pigmentary ferric oxides. Reddening progresses as the diagenetic alteration becomes more advanced, and is thus a time-dependent mechanism. The other implication is that reddening of this type is not specific to a particular depositional environment. However, the favourable conditions for diagenetic red bed formation i.e. positive Eh and neutral-alkaline pH are most commonly found in hot, semi-arid areas, and this is why red beds are traditionally associated with such climates. [7] [8]

Secondary red beds

Secondary red beds are characterized by irregular color zonation, often related to sub-unconformity weathering profiles. The color boundaries may cross-cut lithological contacts and show more intense reddening adjacent to unconformities. Secondary reddening phases might be superimposed on earlier formed primary red beds in the Carboniferous of the southern North Sea. [9] Post-diagenetic alteration may take place through reactions such as pyrite oxidation:

3O2 + 4FeS2→ Fe2O3 (hematite) + 8S E = −789 kJ/mol

and siderite oxidation:

O2 + 4FeCO3 → 2Fe2O3 (hematite) + 4CO2 E = −346 kJ/mol

Secondary red beds formed in this way are an excellent example of telodiagenesis. They are linked to the uplift, erosion and surface weathering of previously deposited sediments and require conditions similar to primary and diagenetic red beds for their formation. [10]

Panorama of the Flaming Cliffs of Mongolia Image-Resized pan-flaming-cropped2 edit1.jpg
Panorama of the Flaming Cliffs of Mongolia

See also

Related Research Articles

<span class="mw-page-title-main">Hematite</span> Common iron oxide mineral

Hematite, also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of Fe
2O
3. It has the same crystal structure as corundum (Al
2O
3) and ilmenite (FeTiO
3). With this it forms a complete solid solution at temperatures above 950 °C (1,740 °F).

<span class="mw-page-title-main">Sedimentary rock</span> Rock formed by the deposition and cementation of particles

Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles to settle in place. The particles that form a sedimentary rock are called sediment, and may be composed of geological detritus (minerals) or biological detritus. The geological detritus originated from weathering and erosion of existing rocks, or from the solidification of molten lava blobs erupted by volcanoes. The geological detritus is transported to the place of deposition by water, wind, ice or mass movement, which are called agents of denudation. Biological detritus was formed by bodies and parts of dead aquatic organisms, as well as their fecal mass, suspended in water and slowly piling up on the floor of water bodies. Sedimentation may also occur as dissolved minerals precipitate from water solution.

<span class="mw-page-title-main">Banded iron formation</span> Distinctive layered units of iron-rich sedimentary rock that are almost always of Precambrian age

Banded iron formations are distinctive units of sedimentary rock consisting of alternating layers of iron oxides and iron-poor chert. They can be up to several hundred meters in thickness and extend laterally for several hundred kilometers. Almost all of these formations are of Precambrian age and are thought to record the oxygenation of the Earth's oceans. Some of the Earth's oldest rock formations, which formed about 3,700 million years ago (Ma), are associated with banded iron formations.

<span class="mw-page-title-main">Goethite</span> Iron(III) oxide-hydroxide named in honor to the poet Goethe

Goethite is a mineral of the diaspore group, consisting of iron(III) oxide-hydroxide, specifically the α-polymorph. It is found in soil and other low-temperature environments such as sediment. Goethite has been well known since ancient times for its use as a pigment. Evidence has been found of its use in paint pigment samples taken from the caves of Lascaux in France. It was first described in 1806 based on samples found in the Hollertszug Mine in Herdorf, Germany. The mineral was named after the German polymath and poet Johann Wolfgang von Goethe (1749–1832).

<span class="mw-page-title-main">Chert</span> Hard, fine-grained sedimentary rock composed of cryptocrystalline silica

Chert is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a chemical precipitate or a diagenetic replacement, as in petrified wood.

<span class="mw-page-title-main">Diagenesis</span> Physico-chemical changes in sediments occurring after their deposition

Diagenesis is the process that describes physical and chemical changes in sediments first caused by water-rock interactions, microbial activity, and compaction after their deposition. Increased pressure and temperature only start to play a role as sediments become buried much deeper in the Earth's crust. In the early stages, the transformation of poorly consolidated sediments into sedimentary rock (lithification) is simply accompanied by a reduction in porosity and water expulsion, while their main mineralogical assemblages remain unaltered. As the rock is carried deeper by further deposition above, its organic content is progressively transformed into kerogens and bitumens.

<span class="mw-page-title-main">Iron(III) oxide</span> Chemical compound

Iron(III) oxide or ferric oxide is the inorganic compound with the formula Fe2O3. It is one of the three main oxides of iron, the other two being iron(II) oxide (FeO), which is rare; and iron(II,III) oxide (Fe3O4), which also occurs naturally as the mineral magnetite. As the mineral known as hematite, Fe2O3 is the main source of iron for the steel industry. Fe2O3 is readily attacked by acids. Iron(III) oxide is often called rust, since rust shares several properties and has a similar composition; however, in chemistry, rust is considered an ill-defined material, described as hydrous ferric oxide.

<span class="mw-page-title-main">Iron oxide</span> Class of chemical compounds composed of iron and oxygen

Iron oxides are chemical compounds composed of iron and oxygen. Several iron oxides are recognized. Often they are non-stoichiometric. Oxyhydroxides are a related class of compounds, perhaps the best known of which is rust.

<span class="mw-page-title-main">Concretion</span> Compact mass formed by precipitation of mineral cement between particles

A concretion is a hard, compact mass formed by the precipitation of mineral cement within the spaces between particles, and is found in sedimentary rock or soil. Concretions are often ovoid or spherical in shape, although irregular shapes also occur. The word 'concretion' is derived from the Latin concretio "(act of) compacting, condensing, congealing, uniting", itself from con meaning "together" and crescere meaning "to grow".

<span class="mw-page-title-main">Martian spherules</span> Small iron oxide spherules found on Mars

Martian spherules (also known as hematite spherules, blueberries, & Martian blueberries) are small spherules (roughly spherical pebbles) that are rich in an iron oxide (grey hematite, α-Fe2O3) and are found at Meridiani Planum (a large plain on Mars) in exceedingly large numbers.

<span class="mw-page-title-main">Maghemite</span> Iron oxide with a spinel ferrite structure

Maghemite (Fe2O3, γ-Fe2O3) is a member of the family of iron oxides. It has the same formula as hematite, but the same spinel ferrite structure as magnetite (Fe3O4) and is also ferrimagnetic. It is sometimes spelled as "maghaemite".

<span class="mw-page-title-main">Iron(III) oxide-hydroxide</span> Hydrous ferric oxide (HFO)

Iron(III) oxide-hydroxide or ferric oxyhydroxide is the chemical compound of iron, oxygen, and hydrogen with formula FeO(OH).

<span class="mw-page-title-main">Ore genesis</span> How the various types of mineral deposits form within the Earths crust

Various theories of ore genesis explain how the various types of mineral deposits form within Earth's crust. Ore-genesis theories vary depending on the mineral or commodity examined.

<span class="mw-page-title-main">Navajo Sandstone</span> Geologic formation in the southwestern United States

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.

<span class="mw-page-title-main">Ferrihydrite</span> Iron oxyhydroxide mineral

Ferrihydrite (Fh) is a widespread hydrous ferric oxyhydroxide mineral at the Earth's surface, and a likely constituent in extraterrestrial materials. It forms in several types of environments, from freshwater to marine systems, aquifers to hydrothermal hot springs and scales, soils, and areas affected by mining. It can be precipitated directly from oxygenated iron-rich aqueous solutions, or by bacteria either as a result of a metabolic activity or passive sorption of dissolved iron followed by nucleation reactions. Ferrihydrite also occurs in the core of the ferritin protein from many living organisms, for the purpose of intra-cellular iron storage.

<span class="mw-page-title-main">Mars surface color</span> Extraterrestrial geography

The surface color of the planet Mars appears reddish from a distance because of rusty atmospheric dust. From close up, it looks more of a butterscotch, and other common surface colors include golden, brown, tan, and greenish, depending on minerals.

<span class="mw-page-title-main">Saprolite</span> Chemically weathered rock

Saprolite is a chemically weathered rock. Saprolites form in the lower zones of soil profiles and represent deep weathering of the bedrock surface. In most outcrops, its color comes from ferric compounds. Deeply weathered profiles are widespread on the continental landmasses between latitudes 35°N and 35°S.

<span class="mw-page-title-main">Iron-rich sedimentary rocks</span> Sedimentary rocks containing 15 wt.% or more iron

Iron-rich sedimentary rocks are sedimentary rocks which contain 15 wt.% or more iron. However, most sedimentary rocks contain iron in varying degrees. The majority of these rocks were deposited during specific geologic time periods: The Precambrian, the early Paleozoic, and the middle to late Mesozoic. Overall, they make up a very small portion of the total sedimentary record.

<span class="mw-page-title-main">Geology of Luxembourg</span>

The geology of Luxembourg is divided into two geologic regions: Rheinisches Schiefergeblige in the north, extending into the Ardennes region in Belgium, and the Oesling Zone to the north of Ettelbruck. The country is underlain by the Hercynian orogeny related Givonne Anticlinorium, which mainly contains Early Devonian sandstone and shale. Rocks closer to the surface are primarily from the Cretaceous and are cut by the Sauer River and its tributaries.

Iron ochre or iron ocher (Ancient Greek: ὠχρός, pale yellow, orange) — at least three iron ore minerals, common abrasives and pigments with a red-brown or brown-orange hue and the powdery consistency of ocher, were known under such a trivial name. The term “iron ocher” was primarily used among mineral collectors, geologists, miners and representatives of related craft professions. It may refer to:

References

  1. ↑ Dictionary of mining, mineral, and related terms (2nd ed.). Alexandria, Va.: American Geological Institute in cooperation with the Society for Mining, Metallurgy, and Exploration, Inc. 1997. ISBN   0-922152-36-5 . Retrieved 8 November 2020.
  2. ↑ Neuendorf, K. K. E.; Mehl, J. P. Jr.; Jackson, J. A., eds. (2005). Glossary of Geology (5th ed.). Alexandria, Virginia: American Geological Institute. ISBN   0-922152-76-4.
  3. ↑ Krynine, P. D. (1950). "Petrology, stratigraphy, and origin of the Triassic sedimentary rocks of Connecticut". Bulletin of the Connecticut Geology and Natural History Survey. 73.
  4. ↑ Van Houten, Franklyn B. (May 1973). "Origin of Red Beds A Review-1961-1972". Annual Review of Earth and Planetary Sciences. 1 (1): 39–61. Bibcode:1973AREPS...1...39V. doi:10.1146/annurev.ea.01.050173.000351.
  5. ↑ Berner, Robert A. (February 1969). "Goethite stability and the origin of red beds". Geochimica et Cosmochimica Acta. 33 (2): 267–273. Bibcode:1969GeCoA..33..267B. doi:10.1016/0016-7037(69)90143-4.
  6. ↑ Langmuir, D. (1 September 1971). "Particle size effect on the reaction goethite = hematite + water". American Journal of Science. 271 (2): 147–156. Bibcode:1971AmJS..271..147L. doi: 10.2475/ajs.271.2.147 .
  7. ↑ Walker, Theodore R. (1967). "Formation of Red Beds in Modern and Ancient Deserts". Geological Society of America Bulletin. 78 (3): 353. doi:10.1130/0016-7606(1967)78[353:FORBIM]2.0.CO;2.
  8. ↑ Walker, Theodore R.; Waugh, Brian; Grone, Anthony J. (1 January 1978). "Diagenesis in first-cycle desert alluvium of Cenozoic age, southwestern United States and northwestern Mexico". GSA Bulletin. 89 (1): 19–32. Bibcode:1978GSAB...89...19W. doi:10.1130/0016-7606(1978)89<19:DIFDAO>2.0.CO;2.
  9. ↑ Johnson, S. A.; Glover, B. W.; Turner, P. (July 1997). "Multiphase reddening and weathering events in Upper Carboniferous red beds from the English West Midlands". Journal of the Geological Society. 154 (4): 735–745. Bibcode:1997JGSoc.154..735J. doi:10.1144/gsjgs.154.4.0735. S2CID   129359697.
  10. ↑ Mücke, Arno (1994). "Chapter 11 Part I. Postdiagenetic Ferruginization of Sedimentary Rocks (Sandstones, Oolitic Ironstones, Kaolins and Bauxites) — Including a Comparative Study of The Reddening of Red Beds". Developments in Sedimentology. 51: 361–395. doi:10.1016/S0070-4571(08)70444-8. ISBN   9780444885173.
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