Figure 21. A high concentration of 

 evenly spaced spherical manganese 

 nodules, 3.48 cm diameter, resting on 

 a Globigerina ooze. Animal churning 

 has caused the partial covering of 

 some nodules. South central Pacific 

 Ocean, northwest of Tahiti. The fresh- 

 ness of the nodule surfaces indicates a 

 low rate of sedimentation in this area. 

 Depth: 3695 m. Photo area: 1.2 m*. 

 1.2 m. Type II camera. 2.6 m target 

 distance. 



A new approach to the problem of manganese nodule 

 concentration at or near the sediment surface has been 

 made by Olausson and Uusitlalo 33 who experimented with 

 artificial sands. They contend that seismic vibrations may 

 cause a lifting effect to keep large particles at the surface 

 for longer times. This, they say, would give rise to high 

 concentrations of nodules at the sediment-water interface 

 and in regions with a comparatively high rate of sedimenta- 

 tion. However, this process would probably not be effective 

 in cohesive clays. In some areas manganese nodules 

 appear to be almost buried as a result of a high rate of 

 sedimentation (fig. 18). 



Type of manganese nodule varies from closely 

 packed spheroids (fig. 21) to widely scattered irregular 

 chunks (fig. 20) and encrusted, irregularly shaped, volcanic 

 rock fragments. In places, manganese oxides have cemented 

 sand surfaces, and closely packed nodules have coalesced 

 to form hard rock surfaces (fig. 16). 



43 



