740 Griffin and golbberg [chap. 26 



of illite, normally associated with high quartz contents. Both of these compo- 

 nents are presumed to originate from the arid regions of the earth and are 

 primarily brought to the oceanic environment by eolian paths. The North Pacific 

 coastal deposits show an enrichment in a " montmorillonite type" mineral 

 which shows evidence of being composed mostly of expandable stripped illite 

 or chlorite. Such clays probably have as their source the coastal continental 

 areas and are mainly transported to the oceans by water paths. Finally, there 

 is a latitudinal decrease in chlorite going from high latitude regions southward, 

 apparently resulting from a chlorite source in the high latitudinal land areas. 



The South Pacific surface samples show little terrestrial influence with 

 montmorillonite being the predominant clay mineral. Apparently this clay 

 arises from the alteration of volcanic materials. In strong association with it is 

 often the zeolite phillipsite. These South Pacific sediments are slowly accumu- 

 lating (0.4 mm/ 103 year on a carbonate -free basis) as compared with their 

 northern mid-ocean counterparts (1-2 mm/lO^ years) which receive large 

 amounts of terrestrial materials. 



The vertical distribution of clay minerals in Recent sediments of the North 

 Pacific is essentially uniform, although a few near-coastal cores show a con- 

 tinuous decrease in montmorillonite relative to illite with depth. The Tertiary 

 deposits of the mid-North Pacific are enriched in montmorillonite and phillip- 

 site and resemble both mineralogically and chemically those of the present-day 

 South Pacific. The South Pacific cores show no recognizable changes in clay- 

 mineral composition with depth in the sedimentary column. 



References 



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 Bates, T. F., F. A. Hildebrand and A. Swineford, 1950. Morphology and structure of 



endellite and halloysite. A^ner. Mineralogist, 35, 463-484. 

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 Bradley, W. F., 1945a. Diagnostic criteria for clay minerals. Amer. Mineralogist, 30, 



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