SECT. 3] PHYSICAL PROPERTIES OF MARINE SEDIMENTS 803 



for a few ocean sediments. He used two disk-shaped samples of like dimensions 

 with a disk-shaped . heat source between them. The sediment samples were 

 confined in ebonite rings. The ends of the sediment disks opposite the heat source 

 were cooled by circulating water. The apparatus was subjected to a vertical 

 load to ensure good thermal contact and the whole apparatus was surrounded 

 by glass wool insulation to reduce loss of heat at the edges. From the dimensions, 

 power input and temperatures at the hot and cold end plates, the thermal 

 conductivity was determined. Zierfuss and van der Vliet (1956) employed a 

 steady-state method to measure thermal conductivity of sedimentary rocks. 

 They also used cylindrical samples but arranged in such a way that all of the 

 heat passing through the sample passed also through a crown glass standard. 

 Thus the only measurements required were of temperature gradient in sample 

 and standard. The ratio of the thermal conductivities is then equal to the in- 

 verse ratio of the temperature gradients. Zierfuss and van der Vliet depended 

 for shielding on a heated glass tube having temperatures at all points very near 

 to those at corresponding points of the sample and standard. In this way 

 edge losses were minimized. 



Von Herzen and Maxwell (1959) measured thermal conductivity on freshly 

 obtained cores by insertion of a small needle probe containing both a heating 

 element and a thermistor. The needle constitutes basically a line source and, 

 after a sufficiently long time, the measm-ed temperature varies linearly with the 

 logarithm of the time. The slope of the line is qj^TrK, where q is the heat input 

 per unit length of cylinder and K is the thermal conductivity. For validity of 

 the linear relationships the time must be large compared with the square of the 

 probe radius divided by the diflfusivity (diffusivity = A'p x thermal capacity). 

 The probe used by Von Herzen and Maxwell was constructed from a hypo- 

 dermic needle 6.4 cm long and 0.086 cm in diameter. The power input was of 

 the order of 2 W and the time required for measurement was 10 min or less. 

 Measurements compared favorably with steady-state measurements carried out 

 on selected samples. For application of measured values to heat-flow deter- 

 mination, corrections for change of temperature and pressure between place of 

 measurement and the sea bottom are required. These corrections are discussed 

 by Bullard et at. (1956). They amount to a 5 to 10% reduction on account of the 

 temperature decrease and something less than a 3% increase to correct for 

 pressure. 



4. Summary of Results 



A. Density-Porosity 



In Fig. 2 are plotted measurements of density as a function of porosity for 

 water-saturated sediments and sedimentary rocks. For a two-component 

 mixture of fluid and particles of a single kind, the relationship is necessarily 

 linear. It is remarkable that when observations are plotted without regard to 

 sediment type the observed points come so close to fitting a single straight fine. 

 In the figure are plotted some 300 points representing measurements on lime- 

 stones, dolomites, sandstones, shales, clays, sands, gravels and ocean sediments. 

 27 — s. Ill 



