SECT. 3] CLAY-MINERAL DISTRIBUTIONS IN THE PACIFIC OCEAN 739 



The first group includes those sediments deposited very rapidly which 

 apparently do not equilibrate with sea-water before burial. However, the 

 majority of cores which penetrate only Recent sediments show no variation 

 in the vertical distribution of clay minerals. 



B. South Pacific 



The few cores examined from the South Pacific showed a uniform vertical 

 distribution. The Mjl ratio was uniform through the depth of sampling. Like 

 the Tertiary sediments in the North Pacific, the 5.0, 4.7, 3.5 and 3.3 A peaks 

 were missing or too diffuse so that their ratios were not amenable to interpreta- 

 tion. The 7.1/10 A ratio could not be used because of the interference of phillip- 

 site. 



It is interesting to note that a core taken from an area in the East Pacific 

 Rise contained no appreciable clay minerals either at the surface or at depth. 

 Samples taken through a length of 9 m did not reveal any indication of clay 

 minerals in diffraction patterns for either the untreated sample or those free 

 of carbonate. Only after removal of iron oxide did any evidence of clay minerals 

 become apparent and then only in trace amounts. 



The homogeneous distribution of clay minerals with depth in any given core 

 emphasizes the stability of clay minerals in the marine environment at least 

 over periods of hundreds of thousands of years. Certainly, the burrowing action 

 of marine organisms may have homogenized the sediments so that subtle 

 changes in composition are smoothed out or are not detectable. Further, it is 

 evident that the physical-chemical environment parameters have not fluctuated 

 with time and that the supply of sediments from the source areas have remained 

 constant within the Recent. 



The older Tertiary sediments from the North Pacific are distinctly similar 

 to the present-day South Pacific ones. The chemical composition (Goldberg and 

 Arrhenius, 1958), the quartz contents (Rex and Goldberg, 1958) and the clay 

 minerals make it inviting to suggest that the North Pacific during Tertiary 

 times was similar as a depositional environment to the South Pacific today, 

 i.e. an area that receives small amounts of detrital minerals and large amounts 

 of pyroclastics. Ross (1955) reported that during the Tertiary Period, the 

 western U.S. received thousands of cubic miles of pyroclastics. No doubt large 

 quantities of this material were ejected into the atmosphere and transported by 

 winds for great distances. If the wind patterns were directed to the west, the 

 North Pacific would receive large quantities of fall-out. With time this fall-out 

 would lose its volcanic identity by reacting with sea-water and altering to 

 montmorillonite or other more stable minerals. 



5. Summary 



The clay-mineral assemblages taken from the surfaces of the marine deposits 



of the Pacific Ocean can be interpreted on the basis of both terrestrial sources 



and authigenic formation. The mid-North Pacific shows marked concentrations 

 25 — s. Ill 



