SECT. 3] CLAY-MINERAL DISTRIBUTIONS IN THE PACIFIC OCEAN 731 



coastal area up to 50°N at which point it becomes > 1, The {C -\-K)jI ratio 

 decreases from vahies around 1 along the coast of Canada, Alaska and the 

 Aleutian Islands to 0.5-1.0 in Mid-Pacific waters. The 3.5/3.3 A peak-area ratio 

 (chlorite + kaolimte)/(ilhte) and the 7.1/10 A were quite similar; however, both 

 ratios were complicated by kaolinite and the former ratio was further compli- 

 cated by quartz (Fig. 4). In order to eliminate these interferences the 4.7/5.0 A 

 ratios were determined (Fig. 2). This plot showed a gradual increase in the ratio 

 with increasing latitude in coastal waters. There is also a decrease in the ratio 

 from the coastal waters off Northern Canada, Alaska and the Aleutians where 

 the ratio is approximately 1.0 to mid-ocean where the ratio is about 0.5. The 

 similarity between the 7.1/10, 3.5/3.3 and 4.5/5.0 A peak-area ratios indicates 

 that chlorite is the varying parameter, not kaolinite. However, the influence of 

 increasing amounts of illite in mid-ocean areas cannot be overlooked and may 

 exert an influence in decreasing the chlorite/ilhte ratio. Isomorphous substi- 

 tution is thought to have little effect since the observed trend is noted in all 

 three peaks, 7.1, 4.7 and 3.5 A. If this effect was present it would show in one 

 of these peak ratios unless this substitution was extremely complex. 



B. South Pacific 



1. Montmorillonite was the most abundant clay mineral in those samples 

 where clay minerals were present. The Mjl ratio was always > 1 and no obvious 

 variation in the ratio with either latitude or longitude was observed (Fig. 1). 



2. Illite was generally present but in much smaller quantities than in the 

 North Pacific. 



3. Kaolinite was present but it was difficult to evaluate its abundance 

 because the 7.1 A peak of kaolinite coincided with one of the strong jDeaks of the 

 zeolite phillipsite. The 4.7 A peak of chlorite was found in the South Pacific in 

 only a few samples (Fig. 2). 



4. The 3.5/3.3 A ratio was variable but with high values clustered near land 

 areas. 



5. In the area between 100-140°W and from the equator to 50°S, which 

 includes the East Pacific Rise, the highly ferruginous and calcareous cores 

 have no detectable clay minerals in the calcium-carbonate-free residue. However, 

 the residue further treated to remove iron oxide (Mehra and Jackson, 1960) 

 contained trace amounts of montmorillonite, illite and chlorite. 



The factors regulating these surface-clay-mineral assemblages can best be 

 approached by some general considerations of marine sedimentation. It is 

 evident from an inspection of maps of the Pacific area that the North Pacific 

 borderlands have more rivers emptying into the ocean and that these rivers 

 have larger drainage basins than do the South Pacific borderlands. Furthermore, 

 the North Pacific Ocean has a larger ratio of land to water area. Quantitative 

 estimates of river- water influx to oceanic areas, based on river lengths, drainage 

 areas, annual rainfalls of land, etc., certainly would enhance our understanding; 

 yet, because the necessary data are either lacking or uncertain in accuracy, 



