SECT. 3] 



PELAGIC SEDIMENTS 



661 



Fig. 3. Mixing by animal burrowing in pelagic sediments. The photograph CH 30 (16-24 

 cm) contains an unusually long vertical worm burrow extending through the section 

 (8 cm). CH 40 (0-8 cm) demonstrates by tone contrast the redistribution of sediment 

 over the boundary between layers of clay and calcareous ooze. 



The section CH 30 (40-48 cm) contains an unconformity between Middle Tertiary 

 and Quaternary sediment. The evaluation of a radioautograph of this section (adjacent 

 to the photograph) distinguishes between the highly alpha-active Quaternary sedi- 

 ment and the inactive Tertiary, and demonstrates the extent and distribution of 

 mixing of material from the two strata. 



The total number of alpha tracks generated in the surface of the section CH 30 

 (40-48 cm) during six weeks was counted, and the average activity in each 4 mm^ 

 surface unit is shown in the radioautograph evaluation in the following intensity 

 shades, graded in vmits of 10~4 alpha particles per cm^ sec: 



No surface tone 0-2.0 



Line hatched 2.1-5.0 



Cross hatched 5.1-9.3 



Double cross hatched 9.4^16.6 



The linear scale in millimeters (relative to an arbitrary origin) is indicated at the edge 

 of the diagram. (From Picciotto and Arrhenius, unpublished.) 



sediments, is the high percentage of authigenic minerals, extra-terrestrial 

 material, and fossil remains of planktonic organisms. Further, with a similar 

 rate of diagenesis in pelagic and neritic deposits, considerably more rapid 

 increase in shear strength with depth in the sediment is found in the former 

 than in the latter (Fig. 4). Bramlette (1961) has pointed out that the redox 



500 



GRAND I. 

 GULF OF 

 MEXICO 



S.D.3.E. ARRHENIUS 0952) 

 EUGENE r 

 GRAND I. 

 S. PASS 



FISK AND 

 MC CLELLAND 



0959) 



MISS. RIVER DELTA 

 S. PASS 



1000 2000 3000 4000 5000 



BURIAL DEPTH, cm 



6000 



7000 



8000 



9000 



Fig. 4. Induration of sediment as a function of burial depth in pelagic sediments (Swedish 

 Deep-Sea Expedition, East Pacific, N. Pacific basin) and in rapidly accumulating 

 clay sediments (max. rate: Miss, delta). (From Moore, 1960.) 



