SECT. 3] CLAY-MINEKAL DISTKIBUTIONS IN THE PACIFIC OCEAN 735 



latitudes (Rex and Goldberg, 1958). The South Pacific is essentially devoid of 

 quartz with abundances rarely exceeding 6% in mid-oceanic areas. These 

 authors attribute the latitudinal dependence to an eolian path for the quartz 

 particles from the arid regions of the continents which have their greatest areal 

 extents in the mid-latitudes of the North Pacific. 



Hurley et al. (1959) point out that the potassium-argon ages of illites taken 

 from the surface sediments of the North Pacific are of the order of hundreds of 

 millions of years old, clearly suggesting a continental source for these clay 

 minerals. 



Finally, the more common occurrences of authigenic minerals, the zeolite 

 phillipsite and the ferromanganese minerals, in sediments from the South 

 Pacific (Goldberg and Arrhenius, 1958) emphasize the significance of in situ 

 mineral formation here. The finding of the large area, the East Pacific Rise, 

 almost free of any detrital minerals is added evidence for a lack of land-derived 

 materials in these sediments. 



Thus, an entry into the understanding of clay-mineral distributions can be 

 initiated with considerations of source areas in the North Pacific and diagenetic 

 processes in the South Pacific. The complexity of the North Pacific clay- 

 mineral assemblages suggests a number of source areas. On the other hand, the 

 rather homogeneous distribution of clay minerals in the South Pacific, combined 

 with the uniformity in chemical and physical properties of near-bottom waters, 

 is not in conflict with a primarily authigenic origin of these materials. 



The formation of montmorillonite from volcanic ash is well documented in 

 the literature (Ross and Hendricks, 1945) and it is quite probable that such an 

 alteration occurs in this area. Furthermore, a few samples examined by 

 electron microscopy and diffraction showed halloysite tubes (Fig. 5), which 

 are found as weathering products of volcanic debris on land. 



The source areas for the clay minerals in the North Pacific may be derived 

 by studying their concentration gradients (Fig. 6). Increasing chlorite abun- 

 dances tend toward the coasts of Canada, Alaska and the Aleutian Islands. 

 Increasing montmorillonite concentrations approach the coastal regions of the 

 east and west Pacific. The implication of source areas for these two minerals 

 from such plots is clear. On the other hand, illite concentrates in mid-ocean 

 areas. This pattern, similar to the quartz band but more diffuse, may well 

 result from an eolian origin from the arid regions of the world for illite. However, 

 because of the much smaller grain size of the clay minerals ( < 2 [x) than the 

 quartz (3-10 [jl), the illite would be subject to a greater dispersion by both 

 atmospheric and oceanic currents. 



The 17 A material found in coastal sediments of the North Pacific may well 

 contain contributions of expandable illites and chlorites. In continental 

 environments where proton attack, oxidation and hydration reactions occur, 

 K+ and Mg2+ can be removed from the inter-layer structures of the illites and 

 chlorites respectively. These stripped clays react like montmorillonite and 

 expand to 17 A under solvation with ethylene glycol. Because these stripped 

 illites and chlorites expand to 17 A in glycol, they have been identified as 



