The term red beds usually refers to strata In geology and related fields, a stratum is a layer of rock or soil with internally consistent characteristics that distinguishes it from contiguous layers. Each layer is generally one of a number of parallel layers that lie one upon another, laid down by natural forces. They may extend over hundreds of thousands of square kilometers of the Earth' of reddish The word red comes from the Old English rēad. Further back, the word can be traced to the Proto-Germanic rauthaz and the Proto-Indo European root reudh-. In Sanskrit, the word rudhira means red or blood. In the English language, the word red is associated with the color of blood, certain flowers , and ripe fruits (e.g. apples, cherries). Fire is-colored sedimentary rocks Sedimentary rock is a type of rock that is formed by sedimentation of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution. Particles that form a sedimentary rock by accumulating such as sandstone Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains. Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any color, but the most common colors are tan, brown, yellow, red, gray and white. Since sandstone beds often form, siltstone Siltstone is a sedimentary rock which has a grain size in the silt range, finer than sandstone and coarser than claystones or shale Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering or bedding less than one centimeter in thickness, that were deposited in hot climates under oxidizing Redox describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed. This can be either a simple redox process, such as the oxidation of carbon to yield carbon dioxide (CO2) or the reduction of carbon by hydrogen to yield methane (CH4), or a complex process such as the oxidation of sugar(C6H12O6) in the conditions.[1] The red color comes from iron oxide Iron oxides are chemical compounds composed of iron and oxygen. Altogether, there are sixteen known iron oxides and oxyhydroxides in their mineral A mineral is a naturally occurring solid chemical substance that is formed through geological processes and that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not have a specific chemical composition structure. Although they have been deposited throughout the Phanerozoic The Phanerozoic Eon is the current eon in the geologic timescale, and the one during which abundant animal life has existed. It covers roughly 545 million years and goes back to the time when diverse hard-shelled animals first appeared. Its name is derived from the Greek words φαίνω and ζωή, meaning make life appear, since it was once, they are most commonly associated with rocks deposited during the Permian The Permian[note 1] is a geologic period and system characterized among land vertebrates by the diversification of the early amniotes into the ancestral groups of the mammals, turtles, lepidosaurs and archosaurs. The Permian Period follows the Carboniferous and extends from 299.0 ± 0.8 to 251.0 ± 0.4 Ma . It is the last period of the Paleozoic and Triassic The Triassic is a geologic period that extended from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events. The extinction event that closed the Triassic Period has recently been more accurately periods.
Red beds have economic significance since many of them contain reservoirs of petroleum Petroleum or crude oil is a naturally occurring, toxic, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights, and other organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling. It is refined and separated, most easily by and natural gas Natural gas is a gas consisting primarily of methane. It is found associated with other fossil fuels, in coal beds, as methane clathrates, and is created by methanogenic organisms in marshes, bogs, and landfills. It is an important fuel source, a major feedstock for fertilizers, and a potent greenhouse gas.
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Primary red beds
Krynine (1950) suggested that the red beds were primarily formed by the erosion and redeposition of red soils or older red beds. A fundamental problem with this hypothesis is the relative scarcity of Permian red colored source sediments to the south of Cheshire Cheshire's area is 2,343 square kilometres and its population is just over a million. Apart from the large towns along the River Mersey and the historic city of Chester, it is mostly rural, with a number of small towns and villages that support an agricultural industry. It is historically famous for the production of Cheshire cheese, salt, bulk. Van Houten (1961) developed the idea to include the in situ (early diagenetic In geology and oceanography, diagenesis is any chemical, physical, or biological change undergone by a sediment after its initial deposition and during and after its lithification, exclusive of surface alteration and metamorphism. These changes happen at relatively low temperatures and pressures and result in changes to the rock's original) reddening of the sediment by the dehydration of brown or drab colored ferric hydroxides. These ferric hydroxides commonly include goethite Goethite (FeO), (pronounced: "Gertite" /ˈgɝtaɪt/) named after the German polymath Johann Wolfgang von Goethe, is an iron bearing oxide mineral found in soil and other low-temperature environments. Goethite has been well known since prehistoric times for its use as a pigment. Evidence has been found of its use in paint pigment samples (FeO-OH) and so called "amorphous ferric hydroxide" or limonite Limonite is an ore consisting in a mixture of hydrated iron oxide-hydroxide of varying composition. The generic formula is frequently written as FeO(OH)·nH2O, although this is not entirely accurate as limonite often contains a varying amount of oxide compared to hydroxide. In fact, much of this material may be the mineral ferrihydrite Ferrihydrite 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 (Fe2O3 H2O).
This dehydration or "aging" process is now known to be intimately associated with pedogenesis Pedogenesis or soil evolution is the process by which soil is created. It is the major topic of the science of pedology, whose other aspects include the soil morphology, classification (taxonomy) of soils, and their distribution in nature, present and past (soil geography and paleopedology) in alluvial Alluvium is loose, unconsolidated (not cemented together into a solid rock), soil or sediments, eroded, deposited, and reshaped by water in some form in a non-marine setting. Alluvium is typically made up of a variety of materials, including fine particles of silt and clay and larger particles of sand and gravel. When this loose alluvial material floodplains A floodplain, or flood plain, is flat or nearly flat land adjacent to a stream or river that experiences occasional or periodic flooding. It includes the floodway, which consists of the stream channel and adjacent areas that carry flood flows, and the flood fringe, which are areas covered by the flood, but which do not experience a strong current and desert A desert is a landscape or region that receives an extremely low amount of precipitation, less than enough to support growth of most plants. Deserts are defined as areas with an average annual precipitation of less than 250 millimetres per year, or as areas where more water is lost by evapotranspiration than falls as precipitation. In the Köppen environments. Berner (1969) showed that goethite Goethite (FeO), (pronounced: "Gertite" /ˈgɝtaɪt/) named after the German polymath Johann Wolfgang von Goethe, is an iron bearing oxide mineral found in soil and other low-temperature environments. Goethite has been well known since prehistoric times for its use as a pigment. Evidence has been found of its use in paint pigment samples (ferric hydroxide) is normally unstable relative to hematite Hematite, also spelled as hæmatite, is the mineral form of iron oxide (Fe2O3), one of several iron oxides. Hematite crystallizes in the rhombohedral system, and it has the same crystal structure as ilmenite and corundum. Hematite and ilmenite form a complete solid solution at temperatures above 950°C and in the absence of water or at elevated temperature will readily dehydrate according to the reaction:
- FeOOH (goethite)→ Fe2O3 (hematite) +H2O
Gibbs Free Energy In thermodynamics, the Gibbs free energy is a thermodynamic potential that measures the "useful" or process-initiating work obtainable from an isothermal, isobaric thermodynamic system. Just as in mechanics, where potential energy is defined as capacity to do work, similarly different potentials have different meanings. Gibbs energy is (G) is defined as some reactions are spontaneous because they give off energy in the form of heat (H In thermodynamics and molecular chemistry, enthalpy is a thermodynamic property of a thermodynamic system. It is used to calculate the heat transfer during a quasistatic process taking place in a closed thermodynamic system under constant pressure (isobaric process). It is also a type of thermodynamic potential. Just as in mechanics, where < 0). Others are spontaneous because they lead to an increase in the disorder of the system (S Entropy is a measure of how disorganized a system is. It is an important part of the second law of thermodynamics. Thermodynamic systems consist of objects, e.g. atoms or molecules, which "carry" energy. In applied thermodynamics, as a matter of convention, entropy is measured in units of energy per temperature . If thermodynamic systems > 0). Calculations of H and S can be used to probe the driving force behind a particular reaction. The Gibbs free energy of a system at any moment in time is defined as the enthalpy In thermodynamics and molecular chemistry, enthalpy is a thermodynamic property of a thermodynamic system. It is used to calculate the heat transfer during a quasistatic process taking place in a closed thermodynamic system under constant pressure (isobaric process). It is also a type of thermodynamic potential. Just as in mechanics, where of the system minus the product of the temperature times the entropy Entropy is a measure of how disorganized a system is. It is an important part of the second law of thermodynamics. Thermodynamic systems consist of objects, e.g. atoms or molecules, which "carry" energy. In applied thermodynamics, as a matter of convention, entropy is measured in units of energy per temperature . If thermodynamic systems of the system.
The Gibbs Free Energy for the reaction goethite ---> hematite (at 250°C) is -2.76kJ/mol and Langmuir (1971) showed that 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 older desert dune sands are more intensely reddened than their younger equivalents.
Diagenetic red beds
The formation of red beds during burial diagenesis was clearly described by Walker (1967) and Walker et al. (1978). The key to this mechanism is the intrastratal alteration of ferromagnesian Mafic is an adjective describing a silicate mineral or rock that is rich in magnesium and iron; the term was derived by contracting "magnesium" and "ferric". Most mafic minerals are dark in color and the relative density is greater than 3. Common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite silicates The silicate minerals make up the largest and most important class of rock-forming minerals, constituting approximately 90 percent of the crust of the Earth. They are classified based on the structure of their silicate group. Silicate minerals all contain silicon and oxygen by oxygenated groundwaters Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of lithologic formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock become completely saturated with water is called during burial. Walker’s studies show that the hydrolysis Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations (H+) (conventionally referred to as protons) and hydroxide anions (OH−) in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by step-growth polymerization. Such polymer of hornblende Hornblende is a complex inosilicate series of minerals . Hornblende is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole. It is an isomorphous mixture of three molecules; a calcium-iron-magnesium silicate, an aluminium-iron-magnesium silicate, and an iron-magnesium silicate and other iron-bearing detritus follows Goldich’s stability series. This is controlled by the Gibbs Free Energy of the particular reaction. For example, the most easily altered material would be olivine The mineral olivine is a magnesium iron silicate with the formula (Mg,Fe)2Si : e.g.
- Fe2SiO4 (fayalite) + O2 → Fe2O3 (hematite) + SiO2 (quartz) with E = -27.53kJ/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 An authigenic mineral or sedimentary rock deposit is one that was generated where it is found or observed. Can be used to characterize metamorphic minerals formed in situ during metamorphism, or to characterize sedimentary minerals formed during sedimentation instead of being transported from elsewhere by water or wind. Authigenic sedimentation is phases. These include mixed layer clays (illite Illite is a non-expanding, clay-sized, micaceous mineral. Illite is a phyllosilicate or layered alumino-silicate. Its structure is constituted by the repetition of tetrahedron – octahedron – tetrahedron layers. The interlayer space is mainly occupied by poorly hydrated potassium cations responsible for the absence of swelling. Structurally – montmorillonite Montmorillonite is a very soft phyllosilicate group of minerals that typically form in microscopic crystals, forming a clay. It is named after Montmorillon in France. Montmorillonite, a member of the smectite family, is a 2:1 clay, meaning that it has 2 tetrahedral sheets sandwiching a central octahedral sheet. The particles are plate-shaped with), quartz Quartz is the second most abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2, potassium feldspar and carbonates Carbonate minerals are those minerals containing the carbonate ion: CO32- as well as the pigmentary ferric oxides Iron oxide is the inorganic compound with the formula Fe2O3. It is of one of the three main oxides of iron, the other two being FeO, which is rare, and Fe3O4, which also occurs naturally as the mineral magnetite. As the mineral known as hematite, Fe2O3 is the main source of the iron for the steel industry. Fe2O3 is paramagnetic, reddish brown, and. 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 In geology, sedimentary depositional environment describes the combination of physical, chemical and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will be formed after lithification, if the sediment is preserved in the rock record. In most cases the environments associated. However, the favourable conditions for diagenetic red bed formation i.e. +Eh Eh is a spoken interjection in English, Armenian, Japanese, French, Italian, Spanish, Portuguese and Catalan that is similar in meaning to "Excuse me?" or "Please repeat that." It is also commonly used as a method for inciting an answer, as in "It's nice here, eh?" It is occasionally used to express indifference, in a and neutral-alkaline pH In chemistry, pH is a measure of the acidity or basicity of a solution. It approximates but is not equal to p[H], the negative logarithm of the molar concentration of dissolved hydronium ions (H3O+); a low pH indicates a high concentration of hydronium ions, while a high pH indicates a low concentration. Crudely, this negative of the logarithm are most commonly found in hot, semi-arid areas, and this is why red beds are traditionally associated with such climates.
Secondary red beds
Secondary red beds are characterized by irregular color zonation, often related to sub-unconformity An unconformity is a buried erosion surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval of time before deposition of the younger, but the term is used to describe any break in the sedimentary geologic record. The weathering Weathering is the breaking down of Earth's rocks, soils and minerals through direct contact with the planet's atmosphere. Weathering occurs in situ, or "with no movement", and thus should not be confused with erosion, which involves the movement of rocks and minerals by agents such as water, ice, wind, and gravity profiles. The color boundaries may cross-cut lithological contacts and show more intense reddening adjacent to unconformities. Johnson et al. (1997) have also showed how secondary reddening phases might be superimposed on earlier formed primary red beds in the Carboniferous The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Ma , to the beginning of the Permian Period, about 299.0 ± 0.8 Ma (ICS, 2004, of the southern North Sea The North Sea is a marginal, epeiric sea on the European continental shelf. The Dover Strait and the English Channel in the south and the Norwegian Sea in the north connect it to the Atlantic Ocean. It is more than 970 kilometres long and 580 kilometres (360 mi) wide, with an area of around 750,000 square kilometres (290,000 sq mi). A large part. The general conditions leading to post-diagenetic alteration have been described by Mücke (1994). Important reactions include pyrite The mineral pyrite, or iron pyrite, is an iron sulfide with the formula Fe 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.
See also
References
- ^ http://www.ac.wwu.edu/~babcock/v2_1.html Ventura Red Beds
- American Geological Institute, Dictionary of Geological Terms, (New York: Dolphin Books, 1962), p. 416.
- Berner R. A., 1969,. Goethite stability and origin of red beds. Geochimica Cosmomochimica Acta, 35, pp 267-273.
- Krynine, P. D., 1950, Petrology, stratigraphy, and origin of the Triassic sedimentary Bulletin of the Connecticut Geology and Natural History Survey, 73, 239p.
- Langmuir, D., 1971, Particle size effect on the reaction Goethite = Hematite + Water. American Journal of Science, 271, pp 147-156.
- Mücke, A., 1994,. Part 1. Postdiagenetic ferruginization of sedimentary rocks (sandstones, oolitic ironstones, kaolins and bauxites) - including a comparative study of the reddening of red beds. [in] Wolf, K. H. and Chilingarian, G V. (eds.) pp 361-395 Diagenesis, IV. Developments in Sedimentology 5 1, Elsevier, Amsterdam.
- Van Houten, F. B., 1973, Origin of red beds. A review -1961-1972. Annual Review Earth Planetary Science, 1, pp 39-61
- Walker, T. R., 1967, Formation of red beds in modern and ancient deserts. Bulletin of the Geological Society of America, 78, pp 353-368.
External links
Categories: Sedimentary rocks
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