806 NAFE AND DRAKE [CHAP. 29 



Ocean basin west of Bermuda. Similar conclusions were reported by Officer 

 (1955) on the basis of wide-angle reflection studies. Hamilton (1956) and Sutton 

 et al. (1957) have observed velocities less than water velocity on recovered 

 sediment samples. Such low velocities are not to be confused with much lower 

 values that occur in gassy sediments. The effect is caused by initial loading of 

 the fluid by particles of higher density in the high-porosity range. Within the 

 experimental error the reduction of velocity is just that predicted by the Wood 

 equation. Lowest measured values are about 1.45 km/sec. 



Porosity is clearly a major factor in determining compressional velocity as 

 Figs. 1 and 3 indicate. The scatter about the main trend may be partially 

 understood by examination of the effects of other variables. Sutton et al. (1957) 

 carried out a detailed study of a group of cores from a variety of environments 

 in the Atlantic Ocean. They measured median grain size, porosity, carbonate 

 content, sorting coefficient, density, average grain density and salt content 

 with the aim of determining separately the influence of each variable on sound 

 velocity. Using a multiple regression analysis involving as variables, porosity, 

 carbonate content and median grain size, they found the velocity to increase 

 with decreasing porosity and increasing grain diameter and carbonate content. 

 Shumway (1960) in a study of a group of samples from the Pacific and Arctic 

 Oceans found a positive connection between velocity and the porosity and 

 between the grain size and porosity. Unlike Shumway's samples those described 

 by Sutton et al. showed no strong correlation between porosity and grain size. 

 Thus the effects of grain size and porosity on velocity could be clearly separated. 



In the high-velocity region shown in Fig. 3 it should be noted that limestones 

 lie for the most part above 4.5 km/sec and sandstones between 3.5 and 5 km/sec. 

 The choice of 6 km/sec for the upper limit of the plotted curves is arbitrary. As 

 the density data will show, some observations on limestones and dolomites 

 occur at velocities as high as 6.5 to 7 km/sec. The dependence of measured 

 velocities on temperature and pressure has been discussed by Shumway (1956) 

 and Sutton et al. (1957). The change with temperature results almost entirely 

 from the change of velocity of the water fraction. Change with temperature 

 for a deep-water sample raised to the surface is approximately the same, though 

 opposite in sign, as the change with pressure. Since bottom- and surface-water 

 velocities differ by about 1% the in situ velocity should differ from that 

 measured on deck by about the same amount. 



C. Compressional Velocity- Density 

 Velocity-density data for sediments and sedimentary rocks are shown in 

 Fig. 4. Included in the figure are results for most of the samples plotted on the 

 velocity-porosity figures. Independent measurements of density were made for 

 most of the ocean sediments occurring in the low-velocity range and for most of 

 the values at very high velocity. Points representing artificially compacted 

 sediments have been derived from measurements of volume of expressed water 

 together with a measurement of initial density. The curve drawn through the 

 points is intended only as a fair indication of the main trend and one that may 



