Misplaced Pages

#965034

23-628: The Hormuz Formation , Hormuz Series , Hormuz Evaporites or Hormuz Group is a sequence of evaporites that were deposited during the Ediacaran (Late Neoproterozoic ) to Early Cambrian , a period previously referred to as the Infra-Cambrian. Most exposures of this sequence are in the form of emergent salt diapirs within anticlines of the Zagros fold and thrust belt . As a result of their involvement in post-depositional salt tectonics ,

46-770: A dozen are common enough to be considered important rock formers. Non-marine evaporites are usually composed of minerals that are not common in marine environments because in general the water from which non-marine evaporite precipitates has proportions of chemical elements different from those found in the marine environments. Common minerals that are found in these deposits include blödite , borax , epsomite , gaylussite , glauberite , mirabilite , thenardite and trona . Non-marine deposits may also contain halite, gypsum, and anhydrite, and may in some cases even be dominated by these minerals, although they did not come from ocean deposits. This, however, does not make non-marine deposits any less important; these deposits often help to paint

69-661: A few percent of evaporite minerals, the remainder being composed of the more typical detrital clastic rocks and carbonates . Examples of evaporite formations include occurrences of evaporite sulfur in Eastern Europe and West Asia. For a formation to be recognised as evaporitic it may simply require recognition of halite pseudomorphs , sequences composed of some proportion of evaporite minerals, and recognition of mud crack textures or other textures . Evaporites are important economically because of their mineralogy, their physical properties in-situ, and their behaviour within

92-437: A picture into past Earth climates. Some particular deposits even show important tectonic and climatic changes. These deposits also may contain important minerals that help in today's economy. Thick non-marine deposits that accumulate tend to form where evaporation rates will exceed the inflow rate, and where there is sufficient soluble supplies. The inflow also has to occur in a closed basin, or one with restricted outflow, so that

115-599: A result of extensional tectonics towards the end of the Pan-African Orogeny . The main structure formed during this period were NW-SE trending dextral (right lateral) strike-slip faults and NE-SW trending extensional faults . Most occurrences of the Hormuz Formation are highly disturbed tectonically. However, a broad stratigraphy has been recognised. Halite layers within the Hormuz sequence form

138-491: Is a chart that shows minerals that form the marine evaporite rocks. They are usually the most common minerals that appear in this kind of deposit. Evaporite minerals start to precipitate when their concentration in water reaches such a level that they can no longer exist as solutes . The minerals precipitate out of solution in the reverse order of their solubilities, such that the order of precipitation from sea water is: The abundance of rocks formed by seawater precipitation

161-595: Is a non- marine evaporite mineral . It is mined as the primary source of sodium carbonate in the United States, where it has replaced the Solvay process used in most of the rest of the world for sodium carbonate production. Turkey is also a major producer. The word entered English by way of either Swedish ( trona ) or Spanish ( trona ), with both possible sources having the same meaning as in English:

184-699: Is covered by a 1.5 m thick trona bed, and occurs in 'salt' pans in the Etosha National Park in Namibia . The Beypazari region in the Ankara Province of Turkey has some 33 trona beds in two fault -bound lensoid bodies in and above oil shales of the Lower Hirka Formation (16 in the lower and 17 in the upper body). The Wucheng basin trona mine, Henan Province China has some 36 trona beds (693–974 m deep),

207-466: Is in the same order as the precipitation given above. Thus, limestone (dolomite are more common than gypsum , which is more common than halite, which is more common than potassium and magnesium salts. Evaporites can also be easily recrystallized in laboratories in order to investigate the conditions and characteristics of their formation. Recent evidence from satellite observations and laboratory experiments suggest evaporites are likely present on

230-722: The Great Salt Lake in Utah and the Dead Sea , which lies between Jordan and Israel. Evaporite depositional environments that meet the above conditions include: The most significant known evaporite depositions happened during the Messinian salinity crisis in the basin of the Mediterranean . Evaporite formations need not be composed entirely of halite salt. In fact, most evaporite formations do not contain more than

253-777: The Makgadikgadi Pans in Botswana and in the Nile Valley in Egypt . The trona near Green River, Wyoming , is the largest known deposit in the world and lies in layered evaporite deposits below ground, where the trona was deposited in a lake during the Paleogene Period. Trona has also been mined at Lake Magadi in the Kenyan Rift Valley for nearly 100 years. The northern part of Lake Natron

SECTION 10

#1732764932966

276-484: The atmosphere for the minerals to precipitate. For this to happen, the water body must enter a restricted environment where water input into this environment remains below the net rate of evaporation. This is usually an arid environment with a small basin fed by a limited input of water. When evaporation occurs, the remaining water is enriched in salts, and they precipitate when the water becomes supersaturated. Marine evaporites tend to have thicker deposits and are usually

299-449: The focus of more extensive research. When scientists evaporate ocean water in a laboratory, the minerals are deposited in a defined order that was first demonstrated by Usiglio in 1884. The first phase of precipitation begins when about 50% of the original water depth remains. At this point, minor carbonates begin to form. The next phase in the sequence comes when the experiment is left with about 20% of its original level. At this point,

322-405: The hydrogen atom in the symmetric (HC 2 O 6 ) anion is disordered. The environment of the disordered H atom was later investigated by Choi and Mighell (1982) at 300 K with three-dimensional single-crystal neutron diffraction: they concluded that the H atom is dynamically disordered between two equivalent sites, separated from one another by 0.211(9) Å. The dynamically disordered H atom

345-740: The internal stratigraphy of the sequence is relatively poorly understood. They are the lateral equivalent of the evaporite-bearing Ara Group in the South Oman Basin . The Hormuz Formation is known from a wide area of the Zagros Mountains and around and beneath the Persian Gulf . Two main depositional basins have been recognised, the North Gulf and South Gulf Basins, separated by the Qatar Arch. The basins were formed as

368-527: The lower 15 beds are 0.5–1.5 m thick, thickest 2.38 m; the upper 21 beds are 1–3 m thick, with a maximum of 4.56 m hosted and underlain by dolomitic oil shales of the Wulidui Formation. Trona has also been found in magmatic environments. Research has shown that trona can be formed by auto metasomatic reactions of late-magmatic fluids or melts (or supercritical fluid -melt mixtures), with earlier crystallized rocks within

391-538: The mineral gypsum begins to form, which is then followed by halite at 10%, excluding carbonate minerals that tend not to be evaporites. The most common marine evaporites are calcite , gypsum and anhydrite , halite, sylvite , carnallite , langbeinite , polyhalite , and kainite . Kieserite (MgSO 4 ) may also be included, which often will make up less than four percent of the overall content. However, there are approximately 80 different minerals that have been reported found in evaporite deposits, though only about

414-604: The mineral natron from North Africa. Both the Spanish and Swedish terms derive from the Arabic trōn , which in turn derives from Arabic natron and Hebrew נתרן ( natruna ), which comes from ancient Greek νιτρον ( nitron ), derived ultimately from ancient Egyptian ntry (or nitry'’). Trona is found at Owens Lake and Searles Lake , California ; the Green River Formation of Wyoming and Utah ;

437-465: The most important decollement level within the Zagros fold and thrust belt. The presence and thickness of the halites has had a major influence on the geometry of the thrust belt and such variations has been used to explain lateral changes in structural style along the belt. Evaporite Although all water bodies on the surface and in aquifers contain dissolved salts, the water must evaporate into

460-491: The same plutonic complex, or by large-scale vapor unmixing in the very final stages of magmatism. The crystal structure of trona was first determined by Brown et al. (1949). The structure consists of units of 3 edge-sharing sodium polyhedra (a central octahedron flanked by septahedra), cross-linked by carbonate groups and hydrogen bonds . Bacon and Curry (1956) refined the structure determination using two-dimensional single-crystal neutron diffraction , and suggested that

483-489: The sediment has time to pool and form in a lake or other standing body of water. Primary examples of this are called "saline lake deposits". Saline lakes includes things such as perennial lakes, which are lakes that are there year-round, playa lakes, which are lakes that appear only during certain seasons, or any other terms that are used to define places that hold standing bodies of water intermittently or year-round. Examples of modern non-marine depositional environments include

SECTION 20

#1732764932966

506-674: The subsurface. Evaporite minerals, especially nitrate minerals, are economically important in Peru and Chile. Nitrate minerals are often mined for use in the production on fertilizer and explosives . Thick halite deposits are expected to become an important location for the disposal of nuclear waste because of their geologic stability, predictable engineering and physical behaviour, and imperviousness to groundwater. Halite formations are famous for their ability to form diapirs , which produce ideal locations for trapping petroleum deposits. Halite deposits are often mined for use as salt . This

529-555: The surface of Titan , Saturn's largest moon. Instead of water oceans, Titan hosts lakes and seas of liquid hydrocarbons (mainly methane) with many soluble hydrocarbons, such as acetylene , that can evaporate out of solution. Evaporite deposits cover large regions of Titan's surface, mainly along the coastlines of lakes or in isolated basins ( Lacunae ) that are equivalent to salt pans on Earth. Trona Trona (trisodium hydrogendicarbonate dihydrate , also sodium sesquicarbonate dihydrate, Na 2 CO 3 ·NaHCO 3 ·2H 2 O)

#965034