Diagenesis of siliceous oozes—I. Chemical controls on the rate of opal-A to opal-CT transformation—an experimental study

摘要: Abstract Evidence from deep-sea sediments supports the following diagenetic maturation sequence: opal-A (siliceous ooze) → opal-CT (porcelanite) chalcedony or cryptocrystalline quartz (chert). A solution-redeposition mechanism is involved in to transformation. Exceptions overall sequence are numerous, suggesting that temperature and time not only important factors controlling these mineralogical transformations. The rates of above transformations strongly affected by composition solution host ; Mesozoic clayey sediments, predominates, while carbonate most common. Experiments at 25 150°C over a period one day six months show transformation rate much higher than clay-rich lepisphere formation aided precipitation nuclei with magnesium hydroxide as an component. role explained follows : carbonate-rich dissolution provides necessary alkalinity, sea water for nuclei. In contrast, clay minerals compete available alkalinity water. As result, clays enriched Mg, reduced. This also bears on common observation replacement silica.