Physical Analysis of Deep Sea Sediments

Abstract

A sonic pulse system, similar to that used at Lamont Geological Observatory for seismic model experiments, was used aboard the Research Vessel VEMA during the summer of 1954 to determine high frequency seismic velocities in fresh deep sea sediment cores. Velocity profiles were obtained from 26 cores covering a wide range of lithologies and ages (Recent to Miocene). Density, porosity, median grain size, sorting, carbonate content, and salt content were also measured. The compressional wave velocity in the ocean‐bottom unconsolidated sediments studied is well represented by the equation: [Formula: see text] where v′=compressional wave velocity in km/sec ϕ=median grain size in phi units γ=percentage of HCl soluble material η=porosity. Many measurements gave velocities less than the velocity of sound in sea water. Most of the low carbonate samples followed a velocity‐porosity relation given by the Wood (1941) equation. The regression coefficient, −.44η, agrees well with the average slope of the Wood equation over the observed porosity range. High carbonate and large median grain size samples gave velocities above that predicted by the Wood equation. These higher velocities are explained as the combined result of shear strength and low effective porosity in the samples. The highest velocities were found in slowly deposited sediments. The degrees of sorting of the sediments had no observable effect on the seismic velocities except that unexplained variations were greater for more poorly sorted materials. No correlation between velocity and age was evident in the sediments studied. The effect of temperature, between 40 and 80°F. on compressional velocity in sediments may be explained by changes in elastic properties of the water fraction alone. The effect of compaction in the upper 15 or 20 feet of homogeneous sediments produced a change in seismic velocity not greater than 1 or 2 percent. Attenuation was greater in the coarse‐grained high‐velocity sediments than in sediments of smaller grain size.

Appendix II. Sediment Physical Properties

“…The application of such corrections is discussed by Hamilton et al (1956), Hamilton (1963;, Sutton et al (1957), Laughton (1954;1957), and Shumway (1958;.…”

“…Velocities in marine sediments have been measured previously under laboratory conditions-and in some cases have included in situ measurement -by Hamilton (1956;1963), Hamilton et al (1956), Laughton (1954;1957), Sutton et al (1957), Shumway (1960), Schreiber (1968), Horn et al (1969), Brier et al (1969), Hamilton et al (1969), and others. These investigations, and Nafe and Drake (1957;1963), related surface sediment sound velocities to other mass physical properties of surface sediments.…”

“…Correlations of porosity and wet-bulk density to other properties of sediment, such as sound velocity, encouraged Hamilton et al (1956), Laughton (1954;1957), Sutton et al (1957), Shumway (1960), Schreiber (1968), Horn et al (1969), Kermabon et al (1969), and Hamilton et al (1969) to collect marine sediment samples and analyze their porosities, densities and other physical properties of the sediments and their interrelationships. Porosity-density interrelationships have been reported with respect to "soil mechanics" of marine sediments (Hamilton, 1959;Moore and Shumway, 1959;Richards, 1962;Hamilton, 1969), heat conductivity in marine sediments (Bullard et al, 1956;Bullard and Day, 1961;Ratcliffe, 1960), and electrical conductivity in marine sediments (Boyce, 1968, andKermabon et al, 1969).…”

Sound Velocity-Density Parameters of Sediment and Rock from DSDP Drill Sites 315–318 on the Line Islands Chain, Manihiki Plateau, and Tuamotu Ridge in the Pacific Ocean

“…For the Leg 33 data a 5% porosity rebound on removal of the uncemented sample from the hole to the laboratory is probably closer to reality than not; therefore, as a very rough estimate, a porosity rebound of 5% will be used for sediment between 30% and 60% porosity, and for lithologies with porosities between 20% and 30% only a 2.5% porosity rebound will be assumed, and below 20% porosity rebound will be considered very small. Of course, near the sediment surface the overburden rebound becomes smaller until it is zero at the sea floor, but fortunately, velocity variations with porosity in these high porosity sediments are also very small (Hamilton, 1959;Nafe and Drake, 1963;Sutton et al, 1957;Shumway, 1960); therefore, it is not a major problem for Leg 33 data (Figure 44).…”

Mass properties of sedimentary rocks and gravimetric effects of petroleum and natural-gas reservoirs

“…Only for the uppermost 1,000 feet of the curve has heavy reliance been placed on data from other sources. For that part of the curve, data of Hamilton and Menard ( 1956), N afe and Drake ( 1957), Sutton, Berckhemer, and Nafe (1957), and Richards ( 1962) form a substantial basis.…”