|
An authigenic mineral or sedimentary rock deposit is one that was generated where it is found or observed. Authigenic sedimentary minerals form during sedimentation by precipitation or recrystallization〔(Authigenic from Oilfield Glossary )〕 instead of being transported from elsewhere (allogenic) by water or wind.〔(Allogenic from Oilfield Glossary )〕 Authigenic sediments are the main constituents of deep sea sedimentation. Authigenic clays tend to reduce the porosity of sediments, thus reducing permeability. Common sedimentary authigenic minerals include calcium carbonate,〔SCOTT RITGER, BOBB CARSON and ERWIN SUESS, 1987. Methane-derived authigenic carbonates formed by subduction-induced pore-water expulsion along the Oregon/Washington margin. Geol. Soc.Am. Bull.; 98; 147-156〕 apatite,〔Kathleen C. Ruttenberg and Robert A. Berner, 1993. Authigenic apatite formation and burial in sediments from non-upwelling, continental margin environments. Geochim. Cosmochim. Acta.; 57; 991-1007〕 and clays.〔M. D. Wilson and E. D. Pittman, 1977. Authigenic clays in sandstones; recognition and influence on reservoir properties and paleoenvironmental analysis. J. Sed. Res.; 47; 3-31.〕 In metamorphic petrology an authigenic mineral is one formed ''in situ'' during metamorphism, again by precipitation from fluids or recrystalisation. For any mineral to be precipitated, the water must be oversaturated with respect to that mineral. For calcite, this means that the area of deposition must be above the carbonate compensation depth, or that the pore waters are sufficiently saturated due to dissolution of other grains that precipitation can begin. The alkalinity can also be reduced by microbial sulphate reduction.〔SCOTT RITGER, BOBB CARSON and ERWIN SUESS, 1987. Methane-derived authigenic carbonates formed by subduction-induced pore-water expulsion along the Oregon/Washington margin. Geol. Soc.Am. Bull.; 98; 147-156〕 ==See also== Neomorphism 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「authigenic」の詳細全文を読む スポンサード リンク
|