142 



HISTORY OF THE OCEANS 





Fig. 7. Vertical sec- 

 tion through the top 

 eight centimeters of a 

 sediment core from the 

 East Equatorial Pacific, 

 showing the mixing of 

 material from adjacent 

 strata by the activity of 

 nuid eating animals. 

 Measurements of the 

 amount of foreign ma- 

 terial present at each 

 level demonstrate that, 

 assuming an originally 

 sharp boundary between 

 the light and dark sedi- 

 ment units, 2-3 cm 

 thick layers below and 

 abo^•e this boundary will 

 ultimately contain 50 

 percent of material origi- 

 nating from the other 

 side of the boundary. 

 The drop of concentra- 

 tion of material origi- 

 nating from a given level 

 with increasing vertical 

 distance from this level 

 is rapid; in only a few 

 cases have single worm 

 channels been obser\ed 

 to penetrate more than 

 20 cm (Picciotto and 

 Arrhenius, unpublished). 



