Chemical controls on the Opal-A to Opal-CT Transformation

Conference · Thu Jan 01 04:00:00 EST 1976

OSTI ID:886869

Kastner, M; Keene, J B

Since early Paleozoic the major mechanisms of silica precipitation at ordinary temperatures and pressures is biochemical. other mechanisms are: adsorption, organo-silicon complexing, evaporation or cooling of silica-rich waters (with subsequent precipitation), and neutralization of strongly alkaline solutions. Evidence from deep-sea sediments supports the following diagenetic sequence Opal-A (siliceous oozes) {yields} Opal-CT (porcelanite) {yields} chalcedony or cryptocrystalline quartz (chert) {yields} mega-quartz (chert). A solution and precipitation mechanism is involved in the above first two transformations. Exceptions to the overall maturation sequence are numerous, suggesting that temperature (burial depth) and time are not the only important factors that control the transformation of Opal-A to Opal-CT. The kinetics of the above transformations are strongly affected by the composition of the host sediments; in clayey sediments Opal-CT (porcelanite) predominates while in carbonate sediments quartz (chert) predominates. There is no simple way to relate either the crystalline state of silica or the texture of porcelanite and chert horizons to the age of surrounding sediments.

• Research Organization: Scripps Institution of Oceanography, La Jolla, CA
• Sponsoring Organization: USDOE
• OSTI ID: 886869
• Report Number(s): COO-2607-4; CONF-760844-14
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
ADSORPTION
CARBONATES
CHERT
EVAPORATION
GEOTHERMAL ENERGY
Geothermal Legacy
KINETICS
MANAGEMENT
PRECIPITATION
QUARTZ
SEDIMENTS
SILICA
TEXTURE
TRANSFORMATIONS