Pelagic Sediments 



M. N. BRAMLETTE* 



Scripps Institution of Oceanography, La Jolla, California 



THE vast extent of pelagic deposits, covering about 70 per cent 

 of the ocean floor, thus about half of the earth, makes them of 

 obvious importance to all earth science. A record, more nearly 

 complete than elsewhere, reflecting many major events of earth 

 history will surely be found through examination of pelagic 

 sediments, especially with their penetration to greater depths. 

 Obviously only a few aspects of the subject, from a geological 

 viewpoint, may be considered in this paper. 



Pelagic sediments seems a useful term although it is not easily 

 defined, as there is a considerable variety of such sediments and, 

 naturally, gradations from pelagic to other sediments. Derivation 

 from pelagos only implies "of the open ocean," but it has been 

 restricted in usage by differentiating such sediments as the 

 hemipelagic sedim.ents bordering major land masses. All the 

 pelagic (eupelagic) sediments, whether largely of plankton remains 

 or fine inorganic particles, have certain distinctive characteristics 

 to reflect their environment of accumulation. Pelagic sediment is 

 precipitated and/or settled from the overlying ocean waters of 

 regions where rates of accumulation are slow enough to cause little 

 change in the great volume of circulating bottom waters, and the 

 little sediment thus accumulates, and normally remains, in a 

 highly oxidized state. This is reflected in their composition and 

 more obviously in the colors of red, brown, and buff. Even the 

 more nearly white oozes, composed largely of plankton remains, 

 show only small parts of the sediment, and these are beneath the 



* Contribution from the Scripps Institution of Oceanography, New Series. This 

 paper is based in part en results of research carried out for the Office of Naval 

 Research. 



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