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Evaporite rock is a sedimentary rock which is normally composed of mineral precipitated from an evaporating saline solution. According to Nely (1994) evaporate rocks are poor in Na and rich in K, with a K/Na ratio higher than in the other rocks. Nely continue to say that when Na is present it is actually concentrated in halite. Nely (1994) established that as one of the major components of evaporate rocks “the potassium rich character of silicates which is analyzed illites rich in potassium and authigenic potassium feldspar is well explained by an equilibrium with a solution having a high potassium and sodium ratio” (p.131).

In their further studies Nely (1994) found out that the rocks which are most typical of evaporate sedimentation is due to their magnesian character and therefore they are the least well marked in regard to boron concentration. There are also the non-sulphate samples of the evaporate rocks which are contrarily very clearly distributed in the magnesium domain delimited by this lines (Nely, 1994). He also noted that for a Fe/Mg ratio of the order of 0.3, the argillites of evaporite rocks are thus distinguished from those of a reference clastic sequence Nely (1994).

Gornitz(2009) on the other hand commented that evaporate deposits can be established through geochemistry which helps in documenting the origin of post-depositional evolution. Gornitz(2009) continues to say that the Br/CI ratios in chloride salts provide information on the evaporite concentrations and the hydrologic history record (p.324). The marine evaporite rocks may have the composition of fluid inclusions of marine halites in the major ion chemistry. Gornitzalso noted that many deposits in the evaporate rock have both marine and non marine influences and alternations between them. These alterations are known to be the result of mixing of marine and non-marine waters in isolated costal lakes and intercalations of continental with costal marine deposits Gornitz(2009).

Environment of deposition (to include tectonic setting). Schreiber, Lugli & Geological Society of London (2007) noted that “a greater thickness of the evaporite formation is present in some wells with a deeper environment of deposition where there is a greater accommodations space” (p.59). They continued to say that such environments have over the time lead to the accumulation and preservation of great thickness of evaporates and they are composed mainly of thick gypsum and anhydrite. These are rich in halite when the conditions are suitable for precipitation of such evaporates.

Anhydrite forms most of the evaporate rocks with some residual gypsum and halite. Schreiber, Lugli, Geological Society of London (2007) also indicated that “the presence of marine organisms in the limestone beds have favored the formation of evaporates with the re-establishment and continuation of restricted marine environmental conditions between evaporate phases” (p.59). They continued to indicate that the intercalated limestone beds within the evaporites are dolomitic and they are highly affected by anhydrization and dissolution hence as e result only ghosts of fossils are preserved.

Modern evaporite deposits as indicated by Gornitz(2009) accumulate in arid and semi-arid regions of the world in the global high pressure belts of the subtropical horse latitude and the poles. In his further studies Gornitz(2009) found out that in the mid-latitude intercontinental desert and steppes that are isolated from oceanic moisture (p. 322). Other arid areas according to Gornitz(2009) where evaporates can form are the rain shadows of high mountain chains which may be present at any latitude. Examples of such areas include Patagonian and Nevada-Utah orographic deserts, which are located in the Andes and the Sierra Nevada rain shadows (Gornitz,2009).

Gornitz(2009) continues to say that the great part of present day evaporite deposition occurs in closed continental basins. He also says that on the other hand coastal settings are volumetrically less significant. Gornitz(2009) also noted that marine evaporates are confined to coastal supratyidal settings and to low lying areas where seawater seeps into pools and small basins. He said that for example small amounts of evaporite minerals are forming in lakes by brine mixing, freezing, evaporation and sublimation.

Condie (1997) states that in attempting to relate mineral and energy deposits to plate tectonics it is important to know the relationship between the deposits and their host rocks (p. 105). According to Condie (1997) tectonic settings for evaporite rocks is characterized by restricted water circulation in which organic matter is preserved. Condie (1997) continued to say that as the rift within this environment continues to open water circulation becomes unrestricted and accumulation of organic matter and evaporite deposition cease. In his research Condie (1997) mentioned that “several requirements must be met in any tectonic setting for the production and accumulation of hydrocarbons such as oil and natural gas” (p. 107).

These conditions include: firstly the preservation of organic matter requires restricted seawater circulation to inhibit oxidations and decompositions. Also high geothermal gradients are needed to convert organic matter into oil and gas (Condie, 1997). Secondly tectonic conditions must be such as to create traps for the hydrocarbons to accumulate. Deformation which accompanies continental collisions creates a variety of structural traps in which hydrocarbons are capable of accumulating. Another example as indicated by Condie (1997) is that coal is formed as a result tectonic settings. These hydrocarbons are as a result of plant remains which must be rapidly buried before they decay were such rapid decays occur in swamps with high plant productivity (Condie, 1997). 

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