Systematic reductions of the porosity of sediments with increasing depth of burial have been attributed--in different degrees by different authors--to increasing effective pressure, increasing temperature, and increasing age. To date, there have been no effective means for determining quantitatively the separate effects of these factors in naturally occurring reductions of porosity. However, limits on the maximum possible effect of each of these factors can be established. This may be done by invoking the logical constraint that in any porosity reduction caused by increasing effective pressure, temperature, and time, the unknown effect of any one factor cannot exceed the known combined effects of all three.

Practical applications of this general principle may be illustrated by using it to establish the maximum possible effect of temperature to test interpretations of porosity-depth curves selected from the literature. In some published interpretations of porosity-depth data, impossibly large effects have been ascribed to temperature. In such cases, porosity reductions thought to have been caused by increased temperature must be attributed instead to some other cause.

Uplift, with erosion of overburden--a common geologic process, could result in a systematic association of lower porosities with higher temperatures, even if porosity were totally unaffected by temperature. Such associations are not cause-and-effect relations and cannot be interpreted correctly as evidence for the dependence of porosity on temperature.