EAS336 Final: Review for EAS 336(Full Year Notes).pdf
19 Apr 2013
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Document Summary
Allogenic- are epiclasts source constituted elsewhere that has been transported. Authogenic- are grown in place(in situ), that is they crystallize. Temperature of crystallization in bowen s reaction series as an indicator of chemical stability of the silicates at atmospheric t/p. ** mechanical instability of micas trumps their chemical stability physical transportation is the cause: glauconite or chamosite. They tend to occur as grain coatings, peloids (occasionally oolitic), microfossil internal molds, microcrystalline micaceous texture. Most common in anoxic diagenesis of sediment deposited on oxegenated aerobic sea floor, thus the iron content e. g. foreland basin: iron oxides and hydroxides. Hematite and limonite form grain coatings/stains to impart distinctive colours to the rocks: silica minerals. Most abundant minerals in most sandstones; estimated at 65%, dominated by q. The shape of q grains can be disguised by syntaxial authogenic overgrowths which have optical continuity to host while hematite preserve outlines and tend to meet at straight non irregular boundaries.
