SKCT. 3] 



PHYSICAL PBOPERTIES OF MARINE SEDIMENTS 



809 



upper limit except at low porosities. Seismic refraction data normally yield 

 values of a higher than 0.25. Limestones at low porosity tend to group around 

 0.30. Evison (1956) has measured a value of ct for concrete of 0.20 at low porosity. 

 Thus considerable scatter may be expected. 



The degree of water saturation is especially important in determining a, for 

 unsaturated sedimentary rocks actually show a decrease of a with increasing 

 porosity rather than an increase as do saturated rocks. 



E. Thermal Coriductivity- Porosity 



Observations of thermal conductivity for ocean sediments and sedimentary 

 rocks are plotted against porosity in Fig. 6. They are compared with computa- 



40 60 



Porosity 



Fig. 6. Thermal conductivity-porosity data for ocean sediments, sandstones and lime- 

 stones compared with theoretical curves adapted from Parasnis (1960). 



tions of Parasnis (1960) for thermal conductivity of mixtures of particles and 

 fluid for two convenient choices of particle shape. The results are applied in one 

 case to the particles of quartz and in the other to calcite. While shape is an 

 important factor there appears also a clear separation of materials according to 

 composition as is shown by the data for sandstones and limestones. 



Conductivities of ocean sediments are principally affected by the water 

 content, as has been pointed out by RatcliflFe (1960) and Bullard et al. (1956). 



F. Selected Values of Other Measured Physical Properties 



Table III provides a selection of values of physical properties for ocean 

 sediments from a number of different marine environments measured by 



