Siliceous skeletal remains, principally of diatoms and radiolarians with smaller amounts of sponge spicules and silicoflagellates, constitute up to approximately 40 percent of some Recent pelagic sediments. The main factors controlling the contribution made by siliceous organisms to marine sediments are apparently (1) the rate of production of siliceous organisms in the overlying waters, (2) the degree of dilution of siliceous remains by terrigenous, volcanic and calcareous organic contributions to the sediment and (3) the extent of solution of the siliceous skeletons, most of which apparently occurs shortly after deposition. Depth of water is apparently not an important direct factor, except insofar as it affects the amount of calcareous contributions to the sediments. The evidence at present available indicates that the production of siliceous organisms is high in the regions of the equatorial current systems and around the edges of the central water masses of the oceans, especially in areas of upwelling, and is much lower in those parts of the oceans in which the near-surface waters are more stably stratified.
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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.