Organic metamorphism--kerogen-to-hydrocarbon transformation--is a function of both temperature and exposure time. The effect of temperature is exponential of that of time linear. At very low temperatures (< 122°F; < 50°C), the conversion rate is so low that time has no effect, since even long time spans of 300 to 500 Ma cannot compensate for this factor. At high temperatures (> 266°F; > 130°C) the reaction proceeds at such a high rate that time also plays no important role. The effect of time is noticeable in the range of 158 to 212°F (70 to 100°C), where intermediate conversion rates prevail.

Stopping the heating process (termination of burial) freezes the rate-constant of the reaction and allows organic metamorphism to continue at a linear rather than exponential rate. This effect is demonstrated with the help of a simple geologic model. For the first example, a source rock was subjected to continuous linear heating, whereas, for the second, the heating was terminated at a certain temperature level. The model was analyzed by using the oleum scale, a modified Lopatin approach.