Diffusimetry (diffusion constant estimation) on sediment cores by resistivity probe

Measurement of formation factor (ratio of rock resistivity to interstitial water resistivity) from sediment cores provides an indirect measurment of the tortuosity of the fluid channels in the sediments. From these measurements one can estimate the diffusion coefficient of the sediment with depth. The F (formation factor) values for Indian Ocean sediments varied from 1.6 for a clayey diatom ooze having 87% porosity (70% water content) to 13.6 for a cemented limestone having 25% porosity (11% water content). These formation factors would yield diffusion coefficients for chloride ions in the corresponding sediments of 6.4 x 10^-6 to 1.5 x 10^-6 cm²/sec. In general, surficial sediments showed diffusion coefficients about one-half to one-third of those for free solution, values decreasing with depth and porosity.