212 



Sediments 



34= I20°00' 



Figure 185. Sediments of Santa Rosa-Cortes Ridge based on 285 samples. Maps show sediment types (symbols as in 

 Fig. 180), median diameter (symbols as in Fig. 175), calcium carbonate (acid-soluble material), and organic matter 

 (1.7 X organic carbon). Dashed hne is 200-meter contour. Adapted from Uchupi (1954). 



in the samples from the flat areas and 20 per 

 cent in the saddle, again doubtlessly a result 

 of a slower rate of sedimentation there. 



Glauconite warrants special discussion 

 here because of its abundance on bank tops. 

 So many papers have been written about 

 glauconite that it is fruitless to attempt to 

 summarize them even briefly. However, 

 most of these papers have attempted to 

 infer the environment of deposition from 

 the scanty evidence remaining long after the 

 enclosing strata had become lithified. Only 

 a few authors have worked with sediments 

 presently being deposited, among whom are 

 Murray and Renard (1891), Galliher (1935), 

 and Takahashi (1939). Although much ad- 

 ditional X-ray and chemical work is desir- 

 able, the greatest lack at present appears to 

 be field and laboratory studies of modern 

 sediments. Where these contain glauconite 

 now being formed, the chances of learning 

 how it forms is far greater than by study of 

 ancient sediments. For this reason some 

 pertinent field and laboratory observations 

 will be presented. 



Field observations show that glauconite 

 is abundant in the same places as phosphorite 



(Fig. 63), — areas in which detrital sediments 

 accumulate very slowly or not at all. The 

 chief associated sediment is foraminiferal 

 sand which with glauconite is enclosed in 

 phosphorite nodules that grow on or in the 

 sediment. Rarely does glauconite comprise 

 more than about 20 per cent of the total 

 sediment, but its color and coarse grain size 

 impart such a unique appearance to the 

 sediment, and its environment of deposition 

 is so diagnostic, that it has an importance 

 beyond that of its percentage abundance. 

 Typically, glauconite occurs on bank tops, 

 ridge crests, hills that rise above shelves, 

 and some slopes. The depths of these en- 

 vironments range from 50 to more than 

 2000 meters. Secondarily, glauconite is 

 present in minor quantities in sand layers 

 interbedded with normal basin sediments; it 

 is assumed that this glauconite has been re- 

 worked from shallow-water areas. 



The environments in which glauconite is 

 abundant are among the most oxygenated 

 of the sea floor, areas of turbulent flow of 

 currents and some movement by waves. 

 Moreover, photographs and samples show 

 the common presence of brittle stars, sea 



