Introduction to Silica in Sediments
Silica occurs as amorphous to crystalline form in many types of igneous, metamorphic, and sedimentary rocks, but in sediments and sedimentary rocks much of the silica is detrital material. The chief forms of silica are hydrous opal, crytocrystalline chalcedony, and crystalline quartz.
The primary aim of this symposium on silica in sediments is chiefly toward the geochemical and organic aspects rather than the study of detrital particles of silica. However, elastic deposits of siliceous organisms, volcanic ash, and other elastics serving as sources of silica are of interest.
Sedimentary silica enters into the development of authigenic quartz and silicates, into clay minerals, and into other secondary compounds as a result of geochemical action. The precipitation of chert, silicification of fossils, formation of skeletal parts and coverings of organisms, cementation of particles, and the relation of silica to diagenesis are matters which warrant research and discussion.
Knowledge of the various aspects of silica in sediments is important economically in regard to mineral deposits, petroleum geology, and ground water. Regeneration of quartz particles, cementation by silica, and differential solution have a great effect on porosity and permeability of aquifers and petroleum reservoirs, thereby reducing or increasing petroleum or water accumulation.
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Silica in Sediments
The Symposium on Silica in Sediments was presented in March, 1958 at the meeting in Los Angeles. The subject was selected by the Research Committee and approval of the Council then proceeded to develop the symposium and organized the papers, and later was authorized to edit and prepare the papers for publication. Cards for written questions directed at the authors of the papers were available during the presentation of the papers. The authors had an opportunity to examine the questions and later to answer them as a panel before those attending the discussion. Additional questions and replies developed between panelists and members of the audience and such were admitted to the discussion for as long a period as seemed feasible within the time available. Written answers to most of the questions were prepared later by the panelists and appear in this publication after respective articles.