OCEANOGRAPHIC INFORMATION FOR SUBMARINE CABLES 



1071 



3.2.2 Sediment Densities 



Quite accurate density determination can be made by laboratory 

 analysis of sediment from core tubes. Densities of 1.35 to 1.55 gm/cc 

 are characteristic of the gray and red clays which cover most of the 

 deeper parts of the ocean. The globigerina oozes which are abundant 

 on the Mid-Atlantic ridge have densities from 1.60 to 1.75 gm/cc. Sand 

 layers which maj^ occur in abyssal plains at or near the sediment surface 

 range in density from 1.65 to 2.00 gm/cc. 



An increase in density as a function of depth in the core would be 

 expected. However, after an initial increase in the first 1 or 2 meters the 

 density usually fails to show further regular increase in cores up to 10 

 meters in length, and deep in the core the density often falls to within 

 0.1 gm/cc of the initial value. 



The sediment averages about 300 fathoms in thickness over the deep 

 ocean floor, except for the bare rock surfaces on the steeper parts of the 

 continental slopes and submarine peaks where sediment is thin or absent. 

 Thicknesses exceeding 100 fathoms may be reached on the continental 

 rises. 



Fig. 12 — Continental -shelf photographs taken off Cape Cod. Each pho- 

 tograph shows an area of approximately 2.4 ft by 3.3 ft. Dials are compas- 

 ses. Tassel beneath dial indicates current. Note small ripple marks in left 

 photograph. Depths : 64 and 54 fathoms, respectively. 



