SECT. 3] 



PELAGIC SEDIMENTS 



707 



crystallites in the ubiquitous fish-bone debris (Fig. 15a) (Arrhenius, Bramlette 

 and Picciotto, 1957), and by the calcite crystallites in foraminiferal tests 

 (Correns, 1937). In the former case higher fatty acids form much of the de- 

 composition products precipitated by salt formation with zinc adsorbed from 

 sea-water. Copper, nickel, lead, and silver, also adsorbed from sea-water, are 

 fixed by the proteinaceous residue in the bone debris, whereas the large amounts 

 of rare-earth elements zirconium and thorium from the same source replace 

 calcium in the apatite crystallites. The slow progressive decomposition of the 

 organic matter in the fish debris is further indicated by the gradual disappear- 

 ance of the deep amber color typical of fragments in Recent strata (Bramlette, 



Fig. 35. Variation of carbon and nitrogen concentrations with depth in core Sw 39 from 

 the Galapagos area. The stratigraphic subdivision of this sequence is shown in Fig. 37, 

 and the absokite age of the stratigraphic units is indicated in Fig. 38. (From Arrhenius, 

 1952.) 



unpubhshed). Complete fading of the color has occurred in pelagic fish debris 

 of Tertiary age. 



Variations in geological time of the rate of accumulation of organic matter, 

 large enough to overshadow the diagenetic effects, and the effects of varying 

 dilution with calcium carbonate, have been found only below areas of excep- 

 tionally high productivity such as at the eastern end of the equatorial current 

 system in the Pacific. In this area the ensuing sedimentary strata, representing 

 times of low and high organic productivity at the surface of the ocean, differ 

 by a factor of two in their content of carbon and nitrogen (Fig. 35). A similar 

 stratification might be expected below the Peru Current and the Kuroshio. 

 24 — s. Ill 



