SECT. 3] 



PHYSICAL PROPERTIES OF MARINE SEDIMENTS 



797 



have. From equation 6 (Table II) density is a linear function of porosity 

 provided the individual grains of the sediment are all of one kind. Nafe and 

 Drake (1957) have shown that nearly the same straight line would fit the 

 observations for sandstones, limestones, shales and ocean sediment cores. A 

 ])orosity range of 0.15 to 0.25 means that density is in all likelihood between 

 2.3 and 2.5 g/cm^. Thus the similarity of particle densities in common sediment- 

 forming substances leads to great simplification in empirical description of 

 physical properties. 



.^ 3 



2- 



1.0 



0.8 



0.6 0.4 



Porosity 



0.2 



Fig. 1. Observations of compressional velocity as a function of porosity. The data are 

 compared with the Wood equation, the time-average equation and an empirical 

 equation of Nafe and Drake. Solid points at low velocity represent measurements on 

 ocean sediments. 



Before proceeding to a discussion of methods and the summary of results it 

 is necessary to comment on the small number of actual measurements that 

 have been made. Of reported observations, there are disproportionally many 

 from easily accessible areas, particularly from shallow water. The only in situ 

 measurements other than seismic have been made in depths that permit 

 operations by divers. Precautions against disturbing the sediment samples to 

 be studied are more effective in the case of shallow- water sediments. To include 

 in the discussion of physical properties sufficient information to make possible 

 predictions and estimates of properties not directly observed, some data from 

 bore holes and from artificial compaction experiments are presented. A dis- 

 tinction between observations on actual marine sediments and others of possibly 

 similar character will be maintained throughout the chapter. 



