Bank Tops 



211 



Figure 1 84. Sediments of Cor- 

 tes and Tanner Banks based 

 on 66 samples. Maps show 

 median diameter, calcium car- 

 bonate (acid-soluble material), 

 organic matter (1.7 x organic 

 carbon), and color of sediment 

 (dry). Dashed line is 200-meter 

 contour. Adapted from Holz- 

 man (1952). 



showed that indeed this is true. However, 

 basalt pebbles and cobbles found at 52 sta- 

 tions north of the saddle that divides it into 

 two parts and at only 1 station south of it 

 indicate that coarse debris from the basalt 

 outcrops on Santa Rosa Island was able to 

 make its way across the top of the ridge un- 

 til stopped by the saddle, presumably during 

 a glacial stage of low sea level. The fine- 

 grained material that accumulated subse- 

 quently presents a complex pattern of 

 organic, authigenic, relict, residual, and 

 present-day detrital sediments. The organic 

 sediments consist of coarse shell sand in 

 turbulent shallow water near shore and fine- 

 to-medium foraminiferal sand in deeper 

 water, particularly in the saddle. The occur- 

 rence of calcareous sediments in both shal- 

 low and deep water and their presence as a 

 component in all sediments lead to a high 

 content of calcium carbonate on the ridge — 

 an average of 51 per cent of all sediments 



and still higher percentages in the saddle, 

 which is farthest from the source of inor- 

 ganic sediments (Fig. 185). The coarse grain 

 size of the calcareous sediments, matched 

 also by most noncalcareous ones, leads to 

 low contents of organic matter, as at Cortes 

 and Tanner Banks, with average values of 

 0.85 per cent on the flat areas and about dou- 

 ble that in the saddle with its finer-grained 

 sediments. Relict and residual sediments 

 occur in deep water atop the ridge, and 

 present-day detrital sediments border the 

 shore zone. The bulk of this sediment is 

 quartz and feldspar with ratio of 6 : 1 , a very 

 high ratio as compared with that on Cortes 

 and Tanner Banks. Among the heavy min- 

 erals magnetite is most abundant, 61 per 

 cent, followed by hornblende, 18 per cent, 

 of the total heavies. Glauconite occurs 

 mixed with most of the other sediments but 

 rarely in quantities great enough to be a ma- 

 jor component. It averages about 5 per cent 



