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33-679: The formation consists of highly fossiliferous gray shale and buff calcareous sandstone with some limestone nodules. It overlies the Morrison Formation and is overlain by the Mesa Rica Sandstone . The formation is interpreted as marine shales deposited during the Kiowa-Skull Creek transgression . It is likely the lateral equivalent of the Glencairn Formation . More than 65 marine invertebrate species have been found in

66-579: A hydroxyl radical and a hydroxide ion in the process. This is the Fenton reaction . Iron(III) is then reduced back to iron(II) by another molecule of hydrogen peroxide, forming a hydroperoxyl radical and a proton . The net effect is a disproportionation of hydrogen peroxide to create two different oxygen-radical species, with water (H  + OH ) as a byproduct. The free radicals generated by this process engage in secondary reactions, which can degrade many organic and biochemical compounds. Iron(II)

99-414: A hard, fissile, metamorphic rock known as slate . With continued increase in metamorphic grade the sequence is phyllite , then schist and finally gneiss . Shale is the most common source rock for hydrocarbons ( natural gas and petroleum ). The lack of coarse sediments in most shale beds reflects the absence of strong currents in the waters of the depositional basin. These might have oxygenated

132-444: Is a d center, meaning that the metal has six "valence" electrons in the 3d orbital shell. The number and type of ligands bound to iron(II) determine how these electrons arrange themselves. With the so-called "strong field ligands" such as cyanide , the six electrons pair up. Thus ferrocyanide ( [Fe(CN) 6 ] has no unpaired electrons, meaning it is a low-spin complex. With so-called "weak field ligands" such as water , four of

165-1201: Is accompanied by telogenesis , the third and final stage of diagenesis. As erosion reduces the depth of burial, renewed exposure to meteoric water produces additional changes to the shale, such as dissolution of some of the cement to produce secondary porosity . Pyrite may be oxidized to produce gypsum . Black shales are dark, as a result of being especially rich in unoxidized carbon . Common in some Paleozoic and Mesozoic strata , black shales were deposited in anoxic , reducing environments, such as in stagnant water columns. Some black shales contain abundant heavy metals such as molybdenum , uranium , vanadium , and zinc . The enriched values are of controversial origin, having been alternatively attributed to input from hydrothermal fluids during or after sedimentation or to slow accumulation from sea water over long periods of sedimentation. Fossils , animal tracks or burrows and even raindrop impressions are sometimes preserved on shale bedding surfaces. Shales may also contain concretions consisting of pyrite, apatite , or various carbonate minerals. Shales that are subject to heat and pressure of metamorphism alter into

198-422: Is called fissility . Shale is the most common sedimentary rock. The term shale is sometimes applied more broadly, as essentially a synonym for mudrock , rather than in the narrower sense of clay-rich fissile mudrock. Shale typically exhibits varying degrees of fissility. Because of the parallel orientation of clay mineral flakes in shale, it breaks into thin layers, often splintery and usually parallel to

231-638: Is composed of about 58% clay minerals, 28% quartz, 6% feldspar , 5% carbonate minerals, and 2% iron oxides . Most of the quartz is detrital (part of the original sediments that formed the shale) rather than authigenic (crystallized within the shale after deposition). Shales and other mudrocks contain roughly 95 percent of the organic matter in all sedimentary rocks. However, this amounts to less than one percent by mass in an average shale. Black shales, which form in anoxic conditions, contain reduced free carbon along with ferrous iron (Fe ) and sulfur (S ). Amorphous iron sulfide , along with carbon, produce

264-430: Is evidence that shale acts as a semipermeable medium, allowing water to pass through while retaining dissolved salts. The fine particles that compose shale can remain suspended in water long after the larger particles of sand have been deposited. As a result, shales are typically deposited in very slow moving water and are often found in lakes and lagoonal deposits, in river deltas , on floodplains and offshore below

297-456: Is found in many minerals and solids. Examples include the sulfide and oxide, FeS and FeO. These formulas are deceptively simple because these sulfides and oxides are often nonstoichiometric . For example, "ferrous sulfide" can refer to the 1:1 species (mineral name troilite ) or a host of Fe-deficient derivatives ( pyrrhotite ). The mineral magnetite ("lode stone") is a mixed-valence compound with both Fe(II) and Fe(III), Fe 3 O 4 . Iron(II)

330-455: Is more likely to form nonfissile mudstone than shale. On the other hand, black shales often have very pronounced fissility ( paper shales ) due to binding of hydrocarbon molecules to the faces of the clay particles, which weakens the binding between particles. Lithification follows closely on compaction, as increased temperatures at depth hasten deposition of cement that binds the grains together. Pressure solution contributes to cementing, as

363-452: Is reduced. In addition to this physical compaction, chemical compaction may take place via pressure solution . Points of contact between grains are under the greatest strain, and the strained mineral is more soluble than the rest of the grain. As a result, the contact points are dissolved away, allowing the grains to come into closer contact. It is during compaction that shale develops its fissility, likely through mechanical compaction of

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396-458: Is used instead for iron(III) salts, containing the cation Fe . The word ferrous is derived from the Latin word ferrum , meaning "iron". In ionic compounds (salts), such an atom may occur as a separate cation (positive ion) abbreviated as Fe , although more precise descriptions include other ligands such as water and halides. Iron(II) centres occur in coordination complexes , such as in

429-399: The U.S. Gulf Coast . As sediments continue to accumulate, the older, more deeply buried sediments begin to undergo diagenesis . This mostly consists of compaction and lithification of the clay and silt particles. Early stages of diagenesis, described as eogenesis , take place at shallow depths (a few tens of meters) and are characterized by bioturbation and mineralogical changes in

462-485: The anion ferrocyanide , [Fe(CN) 6 ] , where six cyanide ligands are bound the metal centre; or, in organometallic compounds , such as the ferrocene [Fe(C 2 H 5 ) 2 ] , where two cyclopentadienyl anions are bound to the Fe centre. All known forms of life require iron. Many proteins in living beings contain iron(III) centers. Examples of such metalloproteins include hemoglobin , ferredoxin , and

495-633: The cytochromes . In many of these proteins, Fe(II) converts reversibly to Fe(III). Insufficient iron in the human diet causes anemia . Animals and humans can obtain the necessary iron from foods that contain it in assimilable form, such as meat. Other organisms must obtain their iron from the environment. However, iron tends to form highly insoluble iron(III) oxides/hydroxides in aerobic ( oxygenated ) environment, especially in calcareous soils . Bacteria and grasses can thrive in such environments by secreting compounds called siderophores that form soluble complexes with iron(III), that can be reabsorbed into

528-651: The wave base . Thick deposits of shale are found near ancient continental margins and foreland basins . Some of the most widespread shale formations were deposited by epicontinental seas . Black shales are common in Cretaceous strata on the margins of the Atlantic Ocean , where they were deposited in fault -bounded silled basins associated with the opening of the Atlantic during the breakup of Pangaea . These basins were anoxic, in part because of restricted circulation in

561-563: The Tucumcari Shale to formation rank in 1959. Shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g., kaolin , Al 2 Si 2 O 5 ( OH ) 4 ) and tiny fragments ( silt -sized particles) of other minerals, especially quartz and calcite . Shale is characterized by its tendency to split into thin layers ( laminae ) less than one centimeter in thickness. This property

594-474: The Tucumcari Shale. The macrofossils are mostly bivalves, with some gastropods and ammonoids . Microfossils include ostracods , foraminiferans , and palynomorphs. Species found in the formation include the solitary corals Desmophyllum and Platycyathus , the bivalves Scabrotrigonia , Pteria , Texigryphaea , Botula , and Lopha , and gastropod Turritella . The shells show borings from clionid sponges and acrothoracic barnacles. The unit

627-421: The black coloration. Because amorphous iron sulfide gradually converts to pyrite , which is not an important pigment, young shales may be quite dark from their iron sulfide content, in spite of a modest carbon content (less than 1%), while a black color in an ancient shale indicates a high carbon content. Most shales are marine in origin, and the groundwater in shale formations is often highly saline . There

660-415: The cell. (The other plants instead encourage the growth around their roots of certain bacteria that reduce iron(III) to the more soluble iron(II).) In contrast to iron(III) aquo complexes, iron(II) aquo complexes are soluble in water near neutral pH. Ferrous iron is, however, oxidized by the oxygen in air, converting to iron(III). Typically iron(II) salts, like the " chloride " are aquo complexes with

693-506: The clumps of clay particles produced by flocculation vary in size from a few tens of microns to over 700 microns in diameter. The floccules start out water-rich, but much of the water is expelled from the floccules as the clay minerals bind more tightly together over time (a process called syneresis ). Clay pelletization by organisms that filter feed is important where flocculation is inhibited. Filter feeders produce an estimated 12 metric tons of clay pellets per square kilometer per year along

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726-408: The color of the rock. Red, brown and green colors are indicative of ferric oxide ( hematite – reds), iron hydroxide ( goethite – browns and limonite – yellow), or micaceous minerals ( chlorite , biotite and illite – greens). The color shifts from reddish to greenish as iron in the oxidized ( ferric ) state is converted to iron in the reduced ( ferrous ) state. Black shale results from

759-527: The context of underground coal mining , shale was frequently referred to as slate well into the 20th century. Black shale associated with coal seams is called black metal. [REDACTED] Media related to Shale at Wikimedia Commons Ferrous In chemistry , iron(II) refers to the element iron in its +2 oxidation state . The adjective ferrous or the prefix ferro- is often used to specify such compounds, as in ferrous chloride for iron(II) chloride ( FeCl 2 ). The adjective ferric

792-445: The formulas [Fe(H 2 O) 6 ] , as found in ferrous ammonium sulfate . The aquo ligands on iron(II) complexes are labile. It reacts with 1,10-phenanthroline to give the blue iron(II) derivative: When metallic iron (oxidation state 0) is placed in a solution of hydrochloric acid , iron(II) chloride is formed, with release of hydrogen gas, by the reaction Iron(II) is oxidized by hydrogen peroxide to iron(III) , forming

825-592: The mineral dissolved from strained contact points is redeposited in the unstrained pore spaces. The clay minerals may be altered as well. For example, smectite is altered to illite at temperatures of about 55 to 200 °C (130 to 390 °F), releasing water in the process. Other alteration reactions include the alteration of smectite to chlorite and of kaolinite to illite at temperatures between 120 and 150 °C (250 and 300 °F). Because of these reactions, illite composes 80% of Precambrian shales, versus about 25% of young shales. Unroofing of buried shale

858-433: The narrow Atlantic, and in part because the very warm Cretaceous seas lacked the circulation of cold bottom water that oxygenates the deep oceans today. Most clay must be deposited as aggregates and floccules, since the settling rate of individual clay particles is extremely slow. Flocculation is very rapid once the clay encounters highly saline sea water. Whereas individual clay particles are less than 4 microns in size,

891-415: The original open framework of clay particles. The particles become strongly oriented into parallel layers that give the shale its distinctive fabric. Fissility likely develops early in the compaction process, at relatively shallow depth, since fissility does not seem to vary with depth in thick formations. Kaolinite flakes have less tendency to align in parallel layers than other clays, so kaolinite-rich clay

924-505: The otherwise indistinguishable bedding planes . Non-fissile rocks of similar composition and particle size (less than 0.0625 mm) are described as mudstones (1/3 to 2/3 silt particles) or claystones (less than 1/3 silt). Rocks with similar particle sizes but with less clay (greater than 2/3 silt) and therefore grittier are siltstones . Shales are typically gray in color and are composed of clay minerals and quartz grains. The addition of variable amounts of minor constituents alters

957-817: The presence of greater than one percent carbonaceous material and indicates a reducing environment. Pale blue to blue-green shales typically are rich in carbonate minerals . Clays are the major constituent of shales and other mudrocks. The clay minerals represented are largely kaolinite , montmorillonite and illite. Clay minerals of Late Tertiary mudstones are expandable smectites , whereas in older rocks (especially in mid-to early Paleozoic shales) illites predominate. The transformation of smectite to illite produces silica , sodium , calcium , magnesium , iron and water. These released elements form authigenic quartz , chert , calcite , dolomite , ankerite , hematite and albite , all trace to minor (except quartz) minerals found in shales and other mudrocks. A typical shale

990-444: The richest source rocks may contain as much as 40% organic matter. The organic matter in shale is converted over time from the original proteins, polysaccharides , lipids , and other organic molecules to kerogen , which at the higher temperatures found at greater depths of burial is further converted to graphite and petroleum. Before the mid-19th century, the terms slate , shale and schist were not sharply distinguished. In

1023-433: The sediments, with only slight compaction. Pyrite may be formed in anoxic mud at this stage of diagenesis. Deeper burial is accompanied by mesogenesis , during which most of the compaction and lithification takes place. As the sediments come under increasing pressure from overlying sediments, sediment grains move into more compact arrangements, ductile grains (such as clay mineral grains) are deformed, and pore space

Tucumcari Formation - Misplaced Pages Continue

1056-414: The waters and destroyed organic matter before it could accumulate. The absence of carbonate rock in shale beds reflects the absence of organisms that might have secreted carbonate skeletons, also likely due to an anoxic environment. As a result, about 95% of organic matter in sedimentary rocks is found in shales and other mudrocks. Individual shale beds typically have an organic matter content of about 1%, but

1089-703: Was first described by Jules Marcou in 1858 as Bed E of the Pyramid Mountain section. In 1892, W.F. Cummins described the Jurassic and Cretaceous section at Tucumcari Mountain as the "Tucumcari beds". Dobrovsky and Summerson assigned the unit to the Purgatoire Formation as the Tucumcari Shale Member in 1947. Griggs and Read abandoned the Purgatoire Formation in southeastern New Mexico and raised

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