Chertification

chertification is a diagenetic process that converts carbonate sediments into chert. These cherts are composed of microcrystalline quartz that contains abundant water that is dispersed interstitially between the crystals. In addition to replacing limestones, cherts can replace opal and/or dolomites. They may fill fractures and are derived from groundwaters rich in silica. cherts can form nodules, breccias, beds, dikes, and spheroids.

The setting of their generation is variable, as is their rate and timing. They can be form contemporaneously with sediment deposition close to the sediment water/ or air interface form ground waters occur which are related to volcanism and so are rich in silica. They can also be late diagenetic features created during the migration of deepwater brines rich in silica. Thus chertification is a product of diagenesis that can be response to low temperature silica rich waters or the product of metasomatism related to volcanic extrusion and dyke intrusions. They form siliceous rocks that can arguably be chemical sediments or the products of replacement of pre-existing sediments (chertification) and the development of concretions. chert nodules in limestones have been linked interstitial anoxia, soft-sediment deformation, when the secondary replacement of carbonate by silica can occur. They are also often associated with evaporites.

In deeper waters opaline silica is commonly deposited as the tests of marine organisms that include Radiolarian and/or sponge spicules.to form an important component of marine sediments. After deposition, these oceanic sediments can undergo diagenesis and form cherts that replace pelagic limestones. Thus deep-sea cherts are found both in the central Atlantic and the Pacific Oceans. Post deposition erosion and transportation can lead to the development of siliceous turbidites that represent by bedded cherts derived from the vicinity of ocean ridges.

Wednesday, March 06, 2013
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